The division of athletes into male and female categories for competition is a widely accepted practice and is ordinarily straightforward, requiring no intervention from authorities. However, for reasons ranging from deliberate cheating to complex medical conditions resulting in ambiguous development of sex organs, the controversy of sex verification in athletic events has existed for 70 years. Testing procedures, initially implemented to prevent cheating by men masquerading as women, have produced humiliating outcomes for women athletes who were often for the first time confronted with the possibility that they have one of the disorders of sex development. Sporting authorities have and continue to formulate position stands for the management of such cases. An important missing component in this debate is the sound scientific evidence to determine (a) whether a performance advantage actually exists and (b) how large it might be. The division of competition into separate categories and the large difference in sporting performance between male and female necessitate that sport-governing bodies define the boundaries between the sexes in a just and fair manner for all participating athletes. This review will therefore provide the historical context of the debate and aim to discuss relevant physiological and performance aspects of the sex verification process.