I'm about 6' and weight around 170, a skinny 170 if that makes any sense, and I buy all my O'Neill wetsuits in a medium. They are always a little tough getting on when brand new but the last thing you want is a wetsuit that's too big. You'll be perfect in a medium
i just had that happen to me...only it was for west wetsuits. i won a free west wetsuit and i ordered a small, only when it came to my house and tried it on did i realize it was way too small. i ordered a medium and to be honest i thought i was a xs but ordered the small just in case. im 5'7.5 140 and the small that i ordered that was too small, and it is suppossed to fit 5'8-5'10 135-155lbs. the medium that i got after wards that fits perfectly is supposed to fit between 5'9-5'11 150-170....Doesn't really make any sense, but hey it not fits.
the point im trying to say is, always order a size up if your not sure. it can never hurt
Oneill seems to be true to their size chart
Pinwheel: it does make me feel a little better being that you wear medium and weigh a little more than me.
Maybe the suit has never been tried on, but I was just surprised how hard it was to get the suit over my legs and feet (and I don't have big legs or feet). The short back zip is a little different but that wasnt really the problem.