I have a multiple entry, non-immigrant visa. I'm a bit confused about what, if anything, I have to do when I leave Thailand (just for a trip).

Can I simply leave the Kingdom and return or do I have to fill out some extra forms/apply for anything else? Last year they cancelled my visa when I left the Kingdom and I don't want that to happen again.

There is a sign at Immigration but the English was so bad I couldn't make heads or tails of it.

The question if if you have a multiple non-immirgat visa (still valid) and have to elave the country every 90 dys. As long as the visa is still valid when you return to Thailand you don't have to do anything. Upon return immirgation will give you a new 90 days to stay in Thailand.

Or ar you on a 1 year extension of stay from immirgation. In that case you need to have a re-entry permit to keep your permission to stay alive. That is why last year they cancelled your "visa", which was actually an extension of stay.

Ok, maybe my first posting wasn't very clear.

I had a non-imm visa until August 2012 and, based on that visa, I now have an extension of stay granted until August 2013. This is not about my 90 day reporting, that I understand and can do in BKK.

It really is just about me leaving the Kingdom, on my current visa/extension, and returning again without it being cancelled.

I already have a multiple entry stamp in my passport (for the aforementioned extension). I just want to know, what if anything, I have to do before I leave the Kingdom?

You have a multiple re-entry permit I think, it should say re-entry permit. If you have that and it is still valid (you bought it when you last extended your stay) you don't have to do anything else, just leave the country and be sure to re-enter before August 2013.

When you return to Thailand you have to fill in an arrival card. On the arrival card it asks for your visa number. Here you don't fill in your visa number but your re-entry permit number! Immirgation will next stamp you in till Aug. 2013. (Check the stamp before leaving immirgaiton, mistakes do happen).

You have a multiple re-entry permit I think, it should say re-entry permit. If you have that and it is still valid (you bought it when you last extended your stay) you don't have to do anything else, just leave the country and be sure to re-enter before August 2013.

When you return to Thailand you have to fill in an arrival card. On the arrival card it asks for your visa number. Here you don't fill in your visa number but your re-entry permit number! Immirgation will next stamp you in till Aug. 2013. (Check the stamp before leaving immirgaiton, mistakes do happen).

Thanks! That clears up that question. Much appreciated.