The occurrence of osteoporotic fractures may seriously compromise the quality of life of lung transplant recipients. However, at present, the true risk of osteoporosis in such patients is unknown. We therefore prospectively evaluated bone mass changes in patients undergoing pulmonary transplantation. Bone mineral density (BMD) of lumbar spine (LS), femoral neck (FN) and femoral shaft (FS), as well as whole body bone mineral content (WB-BMC) were measured in 21 consecutive candidates for lung transplantation (9 males and 12 females; mean+/-SD age 47+/-11 yrs). Twelve of the patients had their BMD remeasured within 6 months after surgery, and nine again after 1 year. Before transplantation, BMD at all sites as well as WB-BMC were significantly decreased as compared to the values in young healthy adults, FN being the most affected (FN -25+/-2%; LS, -12+/-4%; FS -9+/-2%, WB-BMC -15+/-4% (mean+/-SEM)). Seven out of 20 adult patients (35%) fulfilled World Health Organization (WHO) criteria for osteoporosis, i.e. BMD more than 2.5 SD below peak bone mass, whereas three had previously been diagnosed as having osteoporotic fractures of the spine or femoral neck. Within 6 months after transplantation, significant bone loss occurred, mostly at the LS level (-4.0+/-1.7%; p=0.04), despite calcium and vitamin D supplementation. Furthermore, two patients had new osteoporotic vertebral fractures. After 1 year, no further bone loss or new osteoporotic fractures were observed. In conclusion, evaluation of bone mass and prevention of bone loss should be considered early before lung transplantation. Further studies are needed to determine the efficacy of antiresorptive drugs on the prevention of accelerated bone loss and vertebral fractures after transplantation.