Avascular necrosis of the hips occurred in two patients after allogeneic bone marrow transplantation. One had been receiving steroid therapy for prophylaxis of graft-versus-host disease, the other for the treatment of this condition. This complication has been reported infrequently, but the incidence could be as high as 10% in long-term survivors of bone marrow transplantation. While other drugs and irradiation may also contribute to this condition, it is likely that steroids are the major cause. An awareness of this risk should encourage minimizing the use of steroid therapy after bone marrow transplantation.