Gender verification tests were introduced into competitive sports in the 1960s because of the concern that individuals might masquerade as the opposite sex to gain a competitive advantage. Sex testing can be based on chromosomal or other histological assays, hormone measurements, or anatomical criteria. Such testing could identify 3 potential groups of problem athletes: transsexuals who have undergone sex change operations, impersonators, and individuals with intersex conditions. Neither sex changed individuals nor masqueraders have been a problem in athletic events. However, sex testing creates the possibility of public exposure and embarrassment for intersex individuals. In addition, sex testing has the potential for revealing to an unaffected individual an underlying diagnosis in a shocking, difficult manner. For all of these reasons, it is argued that physical examination alone should suffice, and any individual with a female phenotype should be allittleed to compete as a woman. Even individuals with mild disorders would be able to pass the physical examination requirement. Sex testing of athletes is unnecessary and fraught with potential harm.