Perthes disease has an incidence of 1 in 4,750 live births ( 1 in 3,000 boy
s, but only 1 in 11,800 girls). Although there is evidence for a genetic pr
edisposition to Perthes disease, more than two family members are rarely af
fected. We report the first recorded case of Perthes disease affecting thre
e female first-degree relatives.