World 800m champion Caster Semenya has been asked by the International Association of Athletics Federations to take a test to prove her gender. Apparently, because she looks somewhat "masculine", and emerged on the athletics scene out of nowhere to become a world champion runner, she couldn't possibly be female.
One of several BBC Sports articles on the subject:
http://news.bbc.co.uk/sport2/hi/athletics/8212078.stm FAIL!