I am 5'10'', 170lb, and size S fit well, but is form fitting compared to more looser cut MTN jerseys. First time out with this and I was soaked to the bone in a rare AZ rain storm, but was still comfortable through a hour of riding with no odd rubbing or chaffing.
Love this jersey. All my beer loving friends are jealous.
Very good quality. The Hamms racing team approved.