I am almost 5'6" and weigh 102 lbs.  I ordered the XS, and they fit well.  The fabric is slightly thinner than I like; the white area on the leg portion is see through, but the white on the waist band is double lined so it isn't see through.  I haven't worn them, yet.  So, I can't attest to how they keep their shape during/after Zumba, weights, step, etc.  For the price, they were a good buy.