The bone mass was measured by dual energy X-ray absorptiometry in 25 survivors of childhood leukaemia or lymphoma (21 with ALL) who had received TBI and allogeneic BMT a median of 8 years ago (range 4-13). Results were compared with local data on 463 healthy controls and 95 survivors of childhood ALL treated without BMT. Adjusted for sex and age, the mean whole-body bone mineral content (BMC) and bone mineral areal density were significantly less than in healthy controls (0.8 and 0.5 s.d. less than predicted). The reduced BMC was caused by a significantly reduced height for age, whereas bone area for height and BMC for bone area were similar to controls. Less bone mass tended to be related to additional cranial irradiation and age above 20 years at follow-up. Controlled for this, the whole-body bone mass seemed to be unrelated to previous chemotherapy and endocrine status at follow-up and tended to be only marginally less in BMT patients than in ALL survivors treated without BMT. In conclusion, 8 years after allogeneic BMT for childhood leukaemia or lymphoma, the whole-body bone mass was only slightly reduced and the size-adjusted bone mass (BMC for bone area) was normal. Bone Marrow Transplantation (2000) 25, 191-196.