To evaluate the influence of non-insulin-dependent diabetes mellitus (NIDDM) on bone mineral density (BMD), we measured BMD in 185 female patients with NIDDM using dual energy X-ray absorptiometry (DEXA). BMD was measured in lumbar vertebrae (L2-4). BMD is slightly higher in the diabetic patients compared with control subjects and bone loss related to menopause starts before the onset of menopause. The BMD of postmenopausal women showed a definite decrease with aging and there was abrupt bone loss after 55 years of age (p < 0.05). In relation to the duration of diabetes, the decrease of BMD for 15 years was 10.0%. BMD was negatively correlated with age, years since menopause (YSM), and disease duration (r = -0.584, r = -0.470, r = -0.186). These results suggest that age, YSM, and the duration of disease appear to be the risk factors for decreased BMD in the diabetic patients.