Yes!!!
What about with a woman?
AHHHHH!
Some poskim hold that this is forbidden!
BUUUUUUT DOOOON'T WORRRRY! Other poskim are lenient. The door could open at any second and you are not in there for very long.
So how long must one be secluded in order to transgress the prohibition. Here we get into trouble because none of the earlier sources ever mention a specific amount of time. Is this because there IS no amount of time and even a second of yichud is forbidden? Maybe, maybe not.
Some poskim say a minute and a half, some say two minutes, some say five minutes, some say the amount of time it takes to perform an act that could produce a child. These are just some of the many opinions. You could write a whole book - שיעור יחוד כהלכתו...
Bottom line - try to avoid it altogether.
:-)
