Are workplace weight loss competitions a good idea? I see people losing weight during the competition, but do they really keep it off afterward?

I've never been involved in one.
I would think it would depend on your mindset at the beginning of the competition.

I would think that if you were only loosing weight to beat everyone else or get some type of tangible reward that you might not sustain your loss after the contest was over.
However:
If you got more from the competiton that just the tangible reward such as feeling better, going down a size or more, better glucoses or A!C, being able to stop some of your medications, etc you might continue after the end of the contest.

If you went into it with the mindset of this is the beginning of a new way of life for me. And you continue with that mindset then once the competition was over you just might continue to stick with your program.

Once the competition was over I would think you'd need to build a support system to motivate you to continue on with your loss.

Thanks for your thoughts, and I think you're right on target about needing a support system. I think that's true in any type of situation.