Because osteoporosis is a common complication of primary biliary cirrhosis, we evaluated the effects of calcitriol (1alpha, 25-dihydroxyvitamin D3) on bone mineral density in 34 women with primary biliary cirrhosis (stage I disease in 16 patients, stage II in 9, stage III in 4, and stage IV in 5). Patients were assigned randomly to receive calcitriol (0.5mg twice a day) or not. Bone mineral density of the lumbar vertebrae was measured by dual-energy X-ray absorptiometry at least twice during a period of 12-43 months. The mean annual change in bone mineral density was 0.1% in the treatment group and -3.1% in the control group. The median annual change (with 25th and 75th percentiles) in bone mineral density was 0.3% (-0.5%, 1.9%) in the treated group and -3.1% (-4.1%, -2.1%) in the control group. This difference between the two groups was significant (P = 0.0007, Mann-Whitney U-test). Our findings suggest that calcitriol prevents bone loss and may be an effective treatment for osteoporosis in patients with primary biliary cirrhosis.