Three restriction fragment length polymorphisms in the vitamin D receptor gene have been associated with a low bone density in twin and female population studies, but no studies have been conducted exclusively in men. We studied 146 normal men aged 20-83 years. Bone density was measured in the spine, hip, whole body and forearm, and the Bsm polymorphism for the vitamin D receptor was detected by the polymerase chain reaction. Men with genotype BB tended to have a lower bone density at all but one site than the other genotypes. In the men < or = 50 years of age bone density in the forearm was 7% lower in the BB than the Bb and bb groups (P = 0.030) but bone mineral content did not differ between the groups. Bone area was greater in the BB genotype at all sites. This was statistically significant in the forearm (P = 0.026). We conclude that BB genotype is associated with lower bone density in men, which may be due to larger bone size rather than reduced bone mass.