The pathology of a specimen of Legg-Calvé-Perthes disease of eighteen months' clinical duration and six months of roentgenographic changes is described. The radiodense center was formed by necrotic bone and bone dust. The center was surrounded by a zone of fibrous tissue and osteoblasts. devoid of bone. and this in turn was encompassed by normal bone. Revitalization of the bone occurred by creeping substitution, largely by membranous ossification. The epiphyseal plate was cracked and buckled and the cartilage cells failed to align and calcify on the epiphyseal surface of both the articular cartilage and epiphyseal plate.