OBJECTIVE To describe the association of non-insulin-dependent diabetes mellitus (NIDDM) with bone mineral density (BMD). METHODS A survey of men and women from an established epidemiologic cohort who were separately screened for diabetes by oral glucose tolerance test between 1984 and 1987 and for osteopenia by BMD measured in 1988-1989. METHODS A community-based population of older adults, Rancho Bernardo, Calif. METHODS The first 627 consecutively seen white men and women aged 55 to 88 years. METHODS Bone density measured by single photon absorptiometry at the ultradistal wrist and midradius and by dual x-ray absorptiometry at the femoral neck and lumbar spine. RESULTS Among the 236 men and 391 women, whose average age was 72 years, 41 men and 39 women had NIDDM, 56 men and 110 women had impaired glucose tolerance, and 139 men and 242 women had normal glucose tolerance. Men with diabetes had BMD levels similar to those men with normal glucose tolerance, whereas women with diabetes had significantly higher BMD levels at all sites than women with normal glucose tolerance. The increased bone density in diabetic women was unexplained by age, obesity, cigarette smoking, alcohol intake, regular physical activity, and the use of diuretics and estrogen. The multiply adjusted mean BMD in women with NIDDM compared with normoglycemic women was 0.600 g/cm2 vs 0.548 g/cm2 at the midradius; 0.265 g/cm2 vs 0.230 g/cm2 at the ultradistal wrist; 0.654 g/cm2 vs 0.610 g/cm2 at the femoral neck; and 0.962 g/cm2 vs 0.859 g/cm2 at the spine. The sex differences were unexplained by survivor bias, prior obesity, or duration of diabetes. Differences were seen in women (but not men) whose diabetes was first detected at the screening evaluation, ie, before drug or dietary treatment. Similarly, in women (but not men) without diabetes increasing BMD levels at all four sites were associated with increasing postchallenge glucose levels independent of age and body mass index. CONCLUSIONS Older women with NIDDM or hyperglycemia had better BMD than women with normal glucose tolerance, independent of differences in obesity and many other risk factors. No differences in bone density by diabetic status were observed in men. We hypothesize that the sex differences may be explained by the greater androgenicity reported in women with hyperglycemic and hyperinsulinemic conditions.