The shirt is so cute & has a very soft material.  I am 5'1" and 110 lbs. & usually wear a small (sometimes xsmall) top.  I ordered a medium & it's perfect because it is fitted but not clingy.  If you want it to fit very close to the body like in the photo and are young & thin, I'd suggest ordering your regular size. The shoulders are pretty narrow...so a small would not have worked for me.  This top is fitted at the waist, so it flatters the figure.....even mine which is almost straight up & down!  I replied "fit as expected" because I expected the medium to fit like I wanted....It actually does run small.