My newly turned 4 yo did this *a lot* last year. It was totally freaky because it started one morning out of the blue, and it was severe. I was really concerned ... but it seemed to wane over the next few weeks until after a few months DH and I suddenly realized that E. wasn't stuttering anymore. He's "relapsed" once or twice in the meantime, and each time it's been a bit better (hasn't started out as severe, and got better more rapidly). I wish I could figure out what the "trigger" is, if there is one ... but like everyone else said, we just tried to go w/ the flow and not make a big deal out of it. It was harder this very last time he started having problems w/ it again, b/c it was frustrating *him*, and he's start crying or just start feeling really angry b/c he couldn't say what he was wanting to say. That made me really sad for him, and it was hard just to sit back and watch him work through it.