amga-
I'm not sure what's going on here, but properly installed jambs have so many nails through them and into the framing that they don't move. Jambs are generally 4-1/2" wide so that they are flush with a wall constructed of a 3-1/2" framing member and two 1/2" thicknesses of sheetrock. How is your wall constructed? Maybe the wall is wider than a standard jamb and someone "finessed" the molding to cover the gap. You could take off all of the molding on the one side, nail in a 1/2" strip to fill the gap, and renail the molding.

Wrote this too late at night - 1/2" is a huge exaggeration - it's more like 1/8" Ha. Sorry. The jamb is the same width as the rest of the jambs in the house. I figured it was nailed but thought if it had moved out of line I could move it back. All the molding on one side is already off. How hard would it be to get a clean edge where the new strip meets the old wood? They're painted so I'm not worried about grains or stains or anything. Is it possible that the walls have settled and brought things out of line? The door closes perfectly.

Okay, took the molding off the other side and it's definitly just off center rather than too narrow. How do I get it back in line? Do I have to take the whole thing off?

If the jamb has shifted in the framing (does this door get slammed by an angry person frequently? ;-)
You can convince it back into the original centered orientation with a block of wood (to protect the millwork) and a decent-sized hammer. The jamb may have been installed seemingly incorrectly to compensate for twisted rough framing. Before changing it, observe if the latch side of the door hits the doorstop sooner at the top or bottom in an amount equal to the 1/8" you say it is off. If it contacts the stop evenly right now, don't change the jamb, it is where it needs to be.
If the jamb has a rabett for the door, you would be able to make the jamb meet the wall, then use a rabett plane to take off material from the stop surface until the door struck evenly.
If the door jamb has an applied stop, you are able to straighten up the jamb, remove the doorstop and reapply it so that it meets the latched door properly.
There you go, three possible solutions.
Casey

awesome. Don't know about the slamming - we've just had the place since june but PO is original owner and raised 5 kids here so I'm guessing that's a possibility :) the door is def. hitting the stop a little earlier on at the top. Not sure how the stop is done, but I'm pretty sure the door and frame are original to the house, so 1959, whatever that's worth. thanks for all the help!!!

amelia

sorry for reviving an old thread, but my 1957 brick ranch with plaster walls has the same door issue, the front door is a 36x80 with a 20 or so inch side lite glass.
the left bottom of the has moved about 3/4 inch out, I am going to try use the hammer to pursuade it back into its place.
fyi: i asked a lowes installer he was not helpful at all

This is not a job that requires a hammer, but some detective work. That amount of offset is not normal. Take off the interior casing and take a look. If the frame is out of plumb, check the wall. If both are out of plumb the same amount the issue is more then the door frame. If the wall is okay then cut the nails holding the frame in it's current position and readjust the offending leg. Don't remve all of them. Leave one at each end and figure out what need to go where cut the nail that's at issue.
Ron