Caster Semenya, a South African 18-year-old, won the 800-metre track running title at the Berlin World Athletics Championships in 2009. Only 3 h later, her gender was being harshly contested. The investigation of the International Association of Athletics Federations (IAAF) was neither discreet nor respectful of her privacy. Caster's case has implications for the ethics of sports and debates about gender and enhancement, and for the philosophical debate about the nature of categories and the classification of people. The IAAF has (...) not disclosed the results of their tests on Caster, and the South African Ministry of Sport has decreed that in any case she can continue running with women in her own country. But could a scientific or medical test offer uncontroversial answers regarding Caster's gender? The concept of ‘gender’ is partly a social construction. The authors argue that ethics may guide science and medicine at addressing such questions. (shrink)