A case of aseptic necrosis of the first metatarsal sesamoid in the both feet was reported and the differentiation between aseptic necrosis and fracture of the sesamoid was briefly discussed. A 36-year-old woman complained of pain on the first metatarsal head of her left foot without episode of injury. The lateral sesamoid was excised. Pain at this site subsided after operation, but the second operation was performed because of pain on the first metatarsal head of the opposite foot. X-ray of both feet showed irregularity, fragmentation and mottled appearance of those fractured sesamoids. Histological examinations revealed both types of lesion: fracture and aseptic necrosis. This case, however, had all characteristic findings of aseptic necrosis of the sesamoid described by Muller, but a deformity of the feet. Then, it seemed that in both sesamoids of this case, aspect necrosis was a primary lesion and the fracture followed.
