A 66-year-old woman with idiopathic osteonecrosis of the first metatarsal head was treated by arthrodesis of the first metatarsophalangeal joint with a good result. The patient had no history of foot injury, no record of corticosteroid administration, no excessive alcohol intake, and no other predisposing conditions for osteonecrosis. Surgical intervention, by removal of the necrotic area followed by metatarsophalangeal joint fusion, alleviated her foot pain.