Fifteen female patients with primary biliary cirrhosis were evaluated for vitamin D status and evidence of metabolic bone disease. Full-thickness iliac crest bone biopsy specimens with histomorphometric analysis after double tetracycline labeling were performed before and after 1 yr of treatment with oral 25-hydroxyvitamin D (100 micrograms/day). Initially, serum 25-hydroxyvitamin D levels were low (less than 15 ng/ml) in 11 of the 15 patients and were increased to normal (greater than 25 ng/ml) in all patients within 3 mo. Serum parathyroid hormone levels were low normal or not detectable in all patients and did not change with therapy. No patient had a fracture during the treatment. No evidence of osteomalacia was found initially or in follow-up study in any patient. Follow-up histomorphometric analysis at the end of the 1-yr treatment showed that bone volume decreased during the study interval despite therapy (p less than 0.001). Photon beam densitometry confirmed the loss in trabecular density of the radius over the study interval (p less than 0.03). The mean fractional osteoid surface was not increased initially and did not change with therapy. The mean linear bone appositional rate as measured by double tetracycline labeling was not decreased initially and did not change with therapy. It was concluded that in moderate to severe primary ciliary cirrhosis, initial 25-hydroxyvitamin D levels are low and are rapidly corrected by oral 25-hydroxyvitamin D. These patients have significant osteoporosis which progresses despite 25-hydroxyvitamin D.