I heard that I should size up and not so sure I should have. I'm 5'6 153lbs and normally wear a M. I was a size 8 but I've gained weight and am in a 10. So I'm right in the middle were some M are too small and some fit. This suit is loose so I think it's a true size L. I believe if I had gotten a M it would have been snug. I love it though. I was worried I'd look pregnant (I'm not) as my daughter said it would. NOT true. I am hoping to loose weight before I go on vacation, if so I'll have to give this away as the bottoms will probably drop off now when wet. I may just order a smaller size.