Evidence is presented that premature fusion of the epiphyses in the long bones of the extremities is a relatively common finding in patients with homozygous thalas-semia who are more than 10 years old. The anomaly was encountered in 11 of 79 cases surveyed, with an incidence of 23% in patients older than 10. The sites of predilection were the proximal end of one or both humeri and the distal end of one or both femurs. The proximal end of the tibia was also involved in 1 instance. No definite involvement of other bones was found. The fusion tended to involve only a segment of the epiphysis: in the humerus, it was apparently situated medially in all cases, while in the femur it was located posteriorly or anteriorly, and in 1 patient probably centrally. Arrested growth in the bone at the site of fusion produced some decrease in its length. In patients in whom the fusion was eccentrically situated in the epiphyseal cartilage plate, a deformity of the bone end resulted, characterized by a tilt of the epiphysis toward the site of fusion: the humeral head was tilted medially in all cases, and the distal femoral epiphysis was tilted posteriorly or anteriorly, according to the position of the fusion. The cause and pathogenesis of the anomaly are not well understood. The clinical significance of the defect varied according to the site of the fusion and the degree of resulting bony deformity.