OBJECTIVE: To investigate the relationship of androgens to regional muscle size and bone mineral density (BMD) in women with polycystic ovary syndrome (PCOS). METHODS: Seventy-one amenorrheic and right-side dominant women with PCOS (mean age ± standard deviation 28.1 ± 6.7 years) were enrolled. Baseline characteristics included age, height, weight, and body mass index (BMI). Regional BMD and lean mass were measured by whole-body scanning with dual-energy x-ray absorptiometry. Serum levels of testosterone, dehydroepiandrosterone sulfate (DHEAS), and androstenedione were measured by radioimmunoassay. Correlations between regional BMD and variables were investigated using a Pearson correlation test and multiple regression analysis. RESULTS: Serum testosterone levels correlated significantly with lean mass of the left arm, right arm, trunk, left leg, and right leg (r = .34, P < .05 to r = .50, P < .01). Regional lean mass correlated significantly with respective regional BMD (r = .30, P < .05 to r = .68, P < .001). These relationships remained significant after adjusting for age, height, and weight. Serum testosterone levels were not correlated with BMD of the bilateral arms and lumbar spine. Although serum testosterone levels correlated with leg BMD (r = .34, P < .05 to r = .45, P < .01), significance did not persist after adjusting for respective regional lean mass. CONCLUSION: Testosterone influences regional BMD through increasing regional muscle mass in women with polycystic ovary syndrome.