OBJECTIVE Little is known about the pattern of age-related bone loss in men, and although androgens are required for optimum bone mass it is not clear whether the fall in bone mass with age in men is related to falling androgens. METHODS Cross-sectional measurement of bone density, at five sites, and markers of bone resorption and formation in 147 normal volunteers aged 20-83 years. METHODS Healthy laboratory workers, hospital staff, their relatives, and husbands of women attending our osteoporosis clinic. METHODS Forearm density (fat corrected), spine L2-L4, femoral neck, Ward's triangle and trochanter density; serum procollagen I C-terminal extension peptide, osteocalcin, bone alkaline phosphatase and collagen I C-terminal telopeptide; fasting urine hydroxyproline/creatinine, pyridinoline/creatinine and deoxy-pyridinoline/creatinine; and free androgen index (FAI), measured as serum testosterone/sex hormone binding globulin. RESULTS Bone loss accelerated at most sites after age 50. There was a significant fall in FAI from the third decade onwards. The levels of all bone markers fell with age. CONCLUSIONS Bone loss in men appears to accelerate from age 50 and is associated with decreased bone formation which may be associated with falling levels of free androgen.