Background The aim of this study was to estimate the bone mass (BM)and bone mineral density (BMD) of the non-dominate forearm and compare these measurements to basic features of somatic structure and habitual physical activity (PA) levels in adult men. Material and methods The study examined 160 men aged 20 to 50, randomly sampled from Warsaw, Poland. Bone mineral density and BM of the forearm was measured with dual energy x-ray absorptiometry. Anthropometric measurements included: height, body mass, and the width of the elbow and wrist of the non-dominant limb. Habitual PA was assessed by the International Physical Activity Questionnaire. Results The men with sufficient to high levels of PA demonstrated normal values for the T-score in the both the distal and proximal forearm measurement sites in more than 90% of participants and more than 50% in the those with sufficient level of PA. In the group with insufficient levels of PA, low values of the T - score indicating osteopenia was found in both the proximal and distal measurement sites, 71% and 80% respectively. Significant, though weak positive correlations were found between BMD, an indicator of T – score, and a both elbow and wrist widths. Conclusions Lack of PA is clearly associated with an increased occurrence of osteopenia and osteoporosis in men. This study supports the notion that osteopenia and osteoporosis is present in younger adult men and that sufficient habitual PA is a important factor to preserve bone health.