This cross-sectional population-based study examined the association of anthropometric and lifestyle risk factors with bone mineral density (BMD) in 218 white ambulatory men aged 50-64 from the Rancho Bernardo, California cohort. BMD was measured at the lumbar spine and hip using dual-energy X-ray absorptiometry and at the ultradistal wrist and midshaft radius of the forearm using single-photon absorptiometry. Body mass index (BMI) was significantly correlated with BMD at all four skeletal sites. Overall, 17.0% of men aged 55-64 were osteopenic (BMD > or = 2 SD below the distribution for ages 50-54) at one skeletal site, 16.5% were osteopenic at two sites, and 13.6% were osteopenic at three or more sites. Men who reported regular exercise had significantly higher BMD levels at the spine and hip. Men meeting the recommended daily allowance (RDA) for calcium intake (> or = 800 g/day) had significantly higher BMD levels at the spine and wrist. Alcohol intake and smoking were associated with differences of borderline significance in BMD at the spine. In analyses adjusted for BMI, weight change, exercise, smoking, drinking, and calcium intake, there was a significant independent age-related decline in BMD at the hip (0.008 g/cm2/year; p = 0.001), at the wrist (0.004 g/cm2; p < 0.01), at the forearm (0.006 g/cm2; p < 0.01), but not at the spine (0.005 g/cm2). These data, although cross-sectional, strongly suggest that age-related bone loss occurs in middle-aged men and that both physical activity and an adequate calcium intake are associated with better bone density.