Smile regretfully....and perhaps another time...I already have all my plans made...
But...is there a reason why you don't want this friend to bring a guest? Think of from that person's standpoint...maybe they want to announce their engagement...perhaps he has a house guest and can't come without the guest...
You are prefectly within your rights to say..."Sorry"... but I would say OK...
BUT.......Actually the person who asked to bring a guest was beyone rude! If he'she had a house guest....she should have told you sorry I won't be able to make it...
You never expand your host's guest list for them...but when someone has committed a faux pas...I try to accomodate them by saying "of course...I will try to borrow another chair and go buy another steak...".
Linda C

Oh, Lindac, you do not, either! :-)

riken, she's right, the person should not have asked. When I am in a situation like that -- say, I'll have a houseguest -- I tell the hosts that we won't be able to come because we have a guest. Then they are not put on the spot as much; they can say either, "Why don't you bring her?" or "Oh, too bad. Next time, then."
I do think that lindac says the most important thing: that you should consider WHY your friend asked this. Not that it will necessarily make a difference in your decision, but just because it may affect how you handle it, how you feel about your friend's manners, or because there may be something that you need to know about your friend, anything from lindac's examples of an engagement or a houseguest to social anxiety about going places alone, fear that you are planning to match him/her up, etc. Or perhaps your friend simply thought it was an extremely casual, larger event, and thought that this might be a good way for someone new to the community to meet some new friends or something.

Anyway, whatever you decide, be nice about it. If you don't want to include the guest's friend, then say regretfully that unfortunately you can't this time (resist the impulse to give reasons). If you do agree to let the guest bring someone, then do it graciously, not in a way that makes him/her feel guilty or embarrassed -- i.e., don't make any jokes about borrowing chairs or otherwise make your friend squirm, even though you are just joking. Remember, you are a host, so try to make your guest feel welcome, not uncomfortable, even before the party starts.

Thanks for your feedback. I did say yes to my friend, got more steaks/shrimp appetizers and AMAZINGLY she did not bring her friend and didn't call to tell me. But at least I feel good about my decision in the matter.

Thanks again!

I honestly don't mind if someone asks to bring a guest to a party I'm having. The more the merrier is my philosophy. However, if it's a dinner where you're counting on an exact number of people, or an intimate gathering, that's really not appropriate. So, it sort of depends on exactly how clear you made it to your friend as to what kind of party it was.

But the kicker IMHO is that after you made arrangements for this extra person, your friend didn't bother to inform you that she wasn't bringing her friend after all! To me, that's really rude.

I'm guessing this friend thought it was a big party and one person more or less wouldn't matter to you, thus the request to bring the guest, and thus the lack of courtesy to let you know that extra guest wasn't coming after all.

If she did know it was an intimate gathering, both asking to bring the extra person and not bothering to tell you that person wasn't coming are rude. No question about it. If she misunderstood the nature of the party, it's still rude to not let you know the other person wasn't coming.

I actually have a policy that I don't reinvite people to my house who say they are coming to a party/event and then don't show up without calling in advance, unless there's a clear reason why they couldn't call. It's just plain rude. And there's no excuse for not picking up the phone for a quick call, I'm sorry, something's come up and I won't be able to make it after all. This person's behavior goes above and beyond that, because she asked you to make accommodations for this extra guest you don't even know, and then didn't extend the extra courtesy when the person wasn't coming.

Two stories here of people not showing up:
1. My son's bar mitzvah - we had an adult party at my house Saturday evening, a sort of open house, with around 80 people expected. That kind of event, with that many people, you sort of expect that some won't come, it's just the way things like that play out. One couple who was expected called me during the party, so apologetic that they couldn't come, they were in the Vet's emergency room with a very sick cat. Can you imagine that they called me right then and there? That's the kind of excuse that certainly could have waited till the next day, but they wanted to make sure I knew they couldn't come.

2. My annual women only party -- usually around 20 attend. These parties require a lot of work on my part, I do a lot of preparation, including personal stuff for each attendee. One woman didn't show up. Didn't bother to call. She emailed me later, much later, on a different topic altogether so I took that opportunity to ask her why she didn't come. Oh, she said, I just wasn't feeling up to it that day. You can bet I scratched her off my invitations list. Oh well, her loss!

Sorry to go on so long! It's just that to me, it's a great honor to be invited to someone's house, whether it's a small gathering or a huge party. And if you don't take that invitation seriously and behave appropriately, before, during and after, well, in my book, that means you don't value the invitation.

I do not think it was rude to ask to bring a guest. Sometimes invitations are ambiguous.

Nowdays informal invitations are often sent to email addys, and it is not clear exactly who is being invited when it is addressed to "NASCARnut2007@whatever.com"

If you sent out a written or printed invitation addressed soley to one person then yes, it was rude.

Unless, the person was *formally engaged* to their fiance, OR living with someone who was their partner. Then, in that case it was rude of you not to include their partner. I mean you wouldn't invite someone and not include their spouse would you? A fiance or domestic partner should also included in an invitation.

If someone brings a guest without permission to a formal event you could get the message across by cutting the steak in half, and the baked potatoe, and the dessert.......heh-heh-heee. They will get the message and you don't even have to say anything. They will feel embarassed. I know that a host should never embarrass a guest but you can use the excuse that you just did not have any other food to serve to the extra guest.

Or, serve them something obviously completely different from the others - like hot dogs. It doesn't have to be hot dogs, just something obviously different from the other guests - like fish, when everybody else is having steak. Just say that you are serving them both the same entree since you didn't think that just one of them wanted to eat the hot dogs/fish/macaroni, so they are both getting them.

There are ways to get the point across and come across as gracious and accomodating. Heh-hehe-heeee.

While I do think it is rude to bring another guest uninvited, following bud wi's "suggestions" are more likely to make you come across as "petty and childish" than "gracious and accommodating". "Gracious and accommodating" is giving the uninvited guest your own meal while quietly eating something else without drawing attention to that fact.
If, for instance, one has a house guest and is invited to a party, the ideal reply is not, "Oh, can I bring a friend?" but, "I'm sorry, I have a house guest staying with me and don't feel comfortable abandoning him/her to his/her own devices while I come to your party. Maybe another time." That leaves the ball in the HOST's court to say either, "Oh, by all means, bring your friend," or alternately, "I'm sorry, but I can't accommodate extra guests for this. Another time." There is no obligation on the host's part to expand their guest list for the convenience of others.
(That said, I have been in the position of being a house guest where my host went to a party to which she had accepted an invitation prior to my arranging my visit. There was no question of her asking if I could accompany her. I did not mind at all being on my own and did something else which I wanted to do.)

I agree with colleen_oz, and bud_wi, I bet you really wouldn't do either of those things (half a steak or a hot dog). I KNOW you know it wouldn't be "gracious and accommodating"!

Besides humiliating the offending guest, consider the effect on all the other, innocent guests. Wouldn't you be totally embarrassed if a host did that when you were there? I would probably say, "Oh, I love hot dogs, please let me trade with you," and be angry at the host for putting us all in such an awkward situation just to indulge petty indignance.

Thanks to everyone for your responses. I would never single out an invited or uninvited guest. I also believe in being accommodating. The 'friend' that the guest wanted to bring was her son's gymnastics coach.. a person she likes to 'party' with. He lives in town and has his own circle of friends. They are not engaged or dating and I have no idea why she wanted to invite him other than, she couldn't make up her mind whether she wanted to come to my get together or not and wanted a back -up plan. As I stated before, she didn't bring him and didn't tell me. I really like this person and knew her during a different point in her life so I am trying to include in her events but she continues to stretch my hospitality. Unfortunately, during most of the evening, she snuck away to Instant message and text message with her other group of friends. I shouldn't care as it is her loss- but I still feel a bit like she should have just declined the invitation and gone physically where her mind was all night. I could have included a guest that really wanted to be there and we would have all had a better time.

Thanks again for your responses.