There are several possible causes for what you describe. Some are diseases but the most common is called blossom end rot or BER and there is much info here about it in the form of a FAQ that discusses the causes and treatment and 100's of discussions on it - especially over on the Growing Tomatoes forum here - that a search pulls up for you to review. See BER Discussions.

The classic symptom is the appearance of a brown leathery looking spot on the bloom end of the tomato. It then progresses to a general rot of the fruit.

Check out the link below for photos and if that is NOT what you are describing, could you provide more details please such as where on the fruit the spot appears, the appearance of the plant itself and the leaves, how old the plants were when the problem developed, and if your plants were in the ground or in containers.

Thanks. I hope this helps.

Dave

Here is a link that might be useful: Blossom end rot photo

these spots arne't necessarily on the blossom end they appear randomly as small spots that keep getting bigger and develop into rotten spots that gradualy go into the tomatoe as it ripens

I'm sorry Dave I haden't read all of your posting , so I only answeard part of your questions ,these spots appeard
after I pick them they looked fine befor that it was when they started to ripen that the spots appeard , I have planted tomatoes for many years and have never seen this befor

And no signs of disease on the plant itself? Check out all the photos at the source linked below and see if you can match one of the pics to yours. Pay special attention to the pics of Anthracnose and Black Mold.

Dave

Here is a link that might be useful: TAMU - Tomato Problem Solver

Thank you for all your help, from what I saw on that link I have both of those problems (alternaria) and (anthracnose)
if I could post a picture you would see both distincted
patterns, the one with the bulls eye effect seems to be the
worst.thank you again , I will be moving my tomatoe patch next year

Marge, moving your tomatoes won't help much since both Early Blight and Anthracnose are spread by fungal spores that travel good distances through the air.

I had the same situation late in the season,from mid-September on. It was a very wet summer, and I did not spray as often as was necessary. Plus, I used Daconil which is a bit weaker in controlling these diseases. The best would be Mancozeb, which I ran out of last year and didn't order more. Next year I will.

I agree with barkeater - moving the bed isn't the solution, using a good quality fungicide on a regular basis is. Fungus disease are just as much airborne as soil born.

I prefer Daconil since it is more commonly available and I follow the label directions to a T but either will work well.

The key is spraying from the day of planting so that the plants are protected consistently.

Plus it isn't an annual problem for many - if dry summers are your norm and this one was exceptionally wet then that is the cause.

Dave