The bone mineral density (BMD) in patients with insulin-dependent diabetes mellitus (IDDM) was evaluated prospectively to assess the course of osteopenia in IDDM. We measured BMD in the lumbar spine, femoral region, and total body calcium in 23 patients aged 21-53 years with IDDM for 2.3 to 20 years using a dual energy X-ray absorptiometry. A second BMD measurement was done after 26.5+/-4.1 months in all patients. The blood glucose control, insulin dosage, and disease duration were also assessed. Eleven patients had osteopenia (1 Z-score below the mean values of normal gender- and age-matched individuals). These patients had a longer IDDM duration (8.6+/-5.1 years in osteopenics versus 4.6+/-3.75 years in non-osteopenics; p=0.03). The blood glucose control and insulin dosage were not significantly different throughout the study. The mean spinal BMD was higher in the second evaluation in both osteopenics (0.91+/-0.12 g/cm2 and 0.96+/-0.09 g/cm2, p=0.035) and non-osteopenics (1.24+/-0.15 g/cm2 and 1.29+/-0.16 g/cm2; p=0.02). In the end of the study, however, the osteopenic group persisted with lower subnormal BMD values than the non-osteopenic group (p < 0.001). The small BMD increment observed in the spine did not correlate with changes in the metabolic control or with IDDM duration, but occurred mainly in patients younger than 30 years old. There was no significant change in the femoral BMD or total body calcium. None of the patients developed or significantly worsened the osteopenia. We conclude that diabetic osteopenia, despite being a complication of high prevalence in IDDM, seems to be non-progressive in the majority of patients. In some patients, the spinal BMD increased during observation and may have been due to achievement of peak bone mass.