Femoral head collapse occurred in a 20-year-old ballet dancer with anorexia nervosa. The patient developed anorexia nervosa at the age of 11 years and had short stature. The condition never resolved, and she developed pain and stiffness in the right hip at the age of 18 years, with documentation of femoral head collapse on roentgenograms a year later. The patient had delayed pubertal maturation with a bone age of 13 years, primary amenorrhea, and hypoestrogenism. Evaluation for metabolic bone disease was negative, and dual-photon absorptiometry showed significantly decreased bone mass with a bone biopsy revealing only diffuse osteoporosis. Possible etiologic mechanisms of osteonecrosis including repetitive microtrauma and various factors predisposing to femoral head collapse in young women required further investigation.