We report the case histories, radiographic and computed tomographic studies, and histologic findings of two children with metachondromatosis who developed avascular necrosis (AVN) of the femoral ossific nucleus. The first was a 9-year-old boy with involvement of both femoral heads; the second was an 8-year-old girl with involvement of her right femoral head. The changes were associated with either exostoses or enchondromalike lesions of the femoral neck. Interference with the integrity of the lateral epiphyseal vessels by these lesions would explain the avascular changes that occurred. The findings in these cases and other reports associating AVN with skeletal dysplasia should encourage treating physicians to analyze carefully a sudden increase in hip pain or rapid radiographic development of femoral head collapse in a child with a skeletal dysplasia. Recognition of true AVN, in contrast to the gradual evolution of head shape change in typical skeletal dysplasia, may change treatment recommendations and prognosis.