Summary. In the present study we describe the incidence, clinical course, and management of avascular necrosis of bone following allogeneic bone marrow transplantation, and identify risk factors related to its development. All patients developing avascular necrosis of bone after allogeneic bone marrow transplantation between January 1974 and September 1992 were included in the analysis and were studied using the Hôpital Saint Louis Bone Marrow Transplant Database and hospital records. 27/727 allogeneic transplant recipients developed avascular necrosis leading to an 8·1% incidence at 5 years, by product limit estimate, ranging from 5% to 11·2%. Symptoms developed 119–1747 d (median 398 d) after transplantation. In these 27 patients a total of 52 joints were affected (mean 1·92 per patient, range 1–7). The hip joint was most often affected (69% of patients). All patients had joint pain that led to diagnosis by means of standard radiographs with or without the help of technetium-99 scans and/or magnetic resonance imaging. All but three patients received steroid therapy for acute graft-versus-host disease. Among 10 factors tested, three were shown to be significantly linked to an increased risk for developing avascular necrosis by multivariate analysis: male gender (relative risk (RR) 4·2, P= 0·002), age older than 16 (RR = 3·87, P= 0·004), and acute graft-versus-host disease requiring steroid therapy (RR = 6·30, P= 0·0002). 10 patients (37%) required joint replacement within 19 months (range 2–42) following diagnosis of avascular necrosis. In conclusion, avascular necrosis of bone is a frequent late complication of allogeneic bone marrow transplantion causing significant morbidity and requiring replacement surgery in one-third of affected patients. In this 18-year single-centre survey, older age, male gender and steroid therapy given for acute graft-versus-host disease were shown to independently increase the risk of avascular necrosis of bone.