Bedwetting Support Group
Bedwetting (or nocturnal enuresis or sleepwetting) is involuntary urination while asleep. It is the normal state of affairs in infancy, but can be a source of embarrassment when it persists into school age or the teen or adult years. Find others who are coping with a bedwetting problem and share your experiences and questions.
Second, I wouldn't hold my breath for a medical cause or solution. You already know the cause - he has an immature bladder. His bladder has matured some over the last couple of years, certainly, but you can be equally certain that there is still a definite gap in maturity between his bladder and those of most 16-year-olds -- it's just not possible to make up for that much lost time. In fact, he will probably have issues with a somewhat underdeveloped bladder for his whole life (as do many of us hear).
Don't despair, though. What has happened is that his bladder DID mature enough to stay dry at night some, if not most, of the time under optimal conditions. Unlike his peers, though, it was *just barely* mature enough to achieve dryness among those circumstances, and so it's perfectly normal and natural to expect that even a small change in his circumstances (could be stress - a very common trigger at his age - or anything else like diet, changing sleep patterns, or even a physical growth spurt) might be enough to "push him over the edge" back into having at least occasional accidents. The good news is that his overall trajectory is still good, and will probably still lead toward fewer and fewer relapses over time, even though he may always have the sporadic bout of wet sheets even in his adult life.
That is a hard pill to swallow, I realize, that this may still happen once in a while in adulthood. We all want a magic pill to make it go away, believe me. But adult bedwetting is actually VERY common, contrary to what doctors might try to foist on you (just look at this site for confirmation!), and furthermore, it is nothing to be ashamed of! It's just a physical body issue, just like asthma or diabetes or anything else - and no one has any control over it.
I'm an adult in my mid 30s now and have had these sporadic accidents my whole life. It's not ideal, by any means. But neither has it ruined my life or stopped me from doing anything I set my mind to do (just like asthma, diabetes or any other condition doesn't stop anyone from doing anything they really set their mind to do).
Maybe it's just me, but I think it's long past time we stopped obsessing about "curing" this condition, and focused instead on accepting ourselves and one another as we are. Watch your fluids and go to the bathroom before bed, sure, but please don't beat yourself up over an accident (and this goes for you and him both!). He has a weak bladder. His friends may have poor digestion, irregular heartbeat, bad eyesight, or 100 other things. We all are what we are, and we have to make the best of what we have.
Just my thoughts. I, for one, hope fervently that this is just a minor bump in the road for him and after a few more weeks he will never have to deal with it again. Realistically, though, I know better than to bet on that. So I hope even more fervently that neither of you allows this condition to define him or ruin his life, whenever or however it does occur. It's not worth that. Not nearly worth it.