Osteoporotic fractures are potential long-term complications of bone marrow transplantation (BMT). We previously reported that bone mineral density (BMD) of patients undergoing allogeneic BMT decreased by 6% to 9% during the first 6 months after BMT and that bone turnover rate was still increased 1 year after BMT. BMT patients do not need lifelong immunosuppressive treatment, which should offer favorable circumstances for the recovery of BMD. Thus, 27 (14 women, 13 men) of 29 long-term survivors of our previous study were invited to a follow-up study at a median of 75 months after BMT. From 12 months after BMT the BMD of the lumbar spine had increased by 2.4% (P = 0.002). The respective changes in femoral sites were +4.1% in the femoral neck (P = 0.087), 4.0% in the trochanter (P = 0.095), +4.7% in Ward's triangle (P = 0.072) and +1.4% in the total hip (P = 0.23). The markers of bone formation, serum osteocalcin and type I procollagen aminoterminal propeptide (PINP) had returned to control levels, but out of the markers of bone resorption the mean level of serum type I carboxyterminal telopeptide (ICTP) was 41% higher (P = 0.0001) and that of urinary type I collagen N-terminal telopeptide/creatinine (NTx) 41% lower (P = 0.0002) in patients than in controls. The mean serum 25-hydroxyvitamin D [25(OH)D] was 33% lower in patients (P = 0.0002), most of whom had hypovitaminosis D [serum 25(OH)D < or = 37 nmol/l]. Except for two, males had serum testosterone level lower than before BMT and four men had hypogonadism. In conclusion, in long-term survivors of allogeneic BMT BMD recovers and bone turnover state normalizes as compared to the situation 1 year after BMT. More attention should be paid to the vitamin D status of all recipients and to possible hypogonadism of male patients.