Patients with osteoporosis have a body mass index (BMI) that is significantly lower than patients with normal bone mineral density (BMD). This study was conducted to examine the associations among age, height, weight, and BMI in patients with discordant regional BMD. For the purpose of this study, discordant regional BMD was defined as having a BMD result that is in the osteoporotic range at one site while being normal at the other sites. Data from 7513 qualifying bone densitometry scans from a suburban Detroit osteoporosis testing center were analyzed. A patient was classified as having generalized osteoporosis if the T-score was < 2.5 at the lumbar spine, femoral neck, and distal radius and normal if the T-score was > 1 at the same three sites. Patients were determined to have discordant low BMD when the T-score was < 2.5 at one site while the T-score was > 1 at the other two sites. Patients with generalized osteoporosis were older (mean age: 72.2 vs 54.7 yr; p < 0.001), shorter (height: 153.1 vs 161.7 cm; p < 0.001) and had lower BMI (23.7 vs 28.5 kg/m(2); p < 0.001) compared with patients with normal BMD. The distal radius was the site where discordant osteoporosis was most prevalent (70 patients, 0.9%). Patients with isolated low distal radius BMD were similar in age (mean age: 70.4 vs 72.2. yr; p = NS), but were taller (height: 158.6 vs 153.1 cm; p < 0.001) and had BMI values that were significantly higher (BMI: 28.7 vs 23.7 kg/m(2); p < 0.001) than patients with generalized osteoporosis. Patients with discordant BMD at the distal radius had anthropometric characteristics that were significantly different from patients with generalized osteoporosis. These differences may represent differences in the etiology of osteoporosis and differential effects on cortical vs trabecular bone.