AS MORPHSUITS ARE MADE OF STRETCHY SPANDEX WE HAVE FOUND THAT ONE SIZE PRETTY MUCH FITS ALL, BUT FOR A PERFECT FIT FOLLOW THIS SIMPLE GUIDE: IF YOU ARE SMALLER THAN 5'4" CHOOSE MEDIUM IF YOU ARE TALLER THAN 5'4" BUT SMALLER THAN 5'10" CHOOSE LARGE IF YOU ARE TALLER THAN 5'10" BUT SMALLER THAN 6'3" CHOOSE EXTRA LARGE IF YOU ARE TALLER THAN 6'3" CHOOSE EXTRA-EXTRA LARGE