The bone mineral density (BMD) at the lumbar spine, proximal femur, and total skeleton was evaluated in 38 men with primary osteoporosis and vertebral fractures. BMD of the patients was significantly reduced over all skeletal areas compared with controls. The Z-score of the lumbar spine (-2.8 +/- 0.9) was less than that of the other areas (P < 0.001) except the legs (-2.5 +/- 1.1) (p.n.s.) showing that bone loss had a tendency to be greater over the axial skeleton. Vertebral dimensions compared with age-matched controls were as follows: projected L2-L4 area (cm 2): 45.7 +/- 5.6 versus 53.7 +/- 3. 6 (P < 0.001); vertebral width (cm): 4.37 +/- 0.44 versus 4.90 +/- 0. 36 (P < 0.001). Serum biochemical parameters and testosterone levels were similar between osteoporotic and control men. We conclude that men with vertebral osteoporotic fractures have reduced vertebral BMD and vertebral dimensions compared with age-matched controls. Thus, these findings indicate that the achievement of a reduced bone size at the end of the growth period or a failure of periosteal increase during adult life is likely to contribute to the pathogenesis of the vertebral fractures observed in older men.