Mineral metabolism was studied in 31 patients with chronic renal failure on continuous ambulatory peritoneal dialysis (CAPD) for a year. After baseline observations, 1-year calcifediol treatment was started in all the patients (100 μg/day). After therapy, progressive normalization of calcium levels was found in all patients, while plasma phosphate did not change. After therapy, plasma alkaline phosphatase and parathyroid hormone decreased significantly. 1,25-Dihydroxyvitamin D showed a slight increase, and 25-hydroxyvitamin D (extremely low at the start of the study) rose, reaching normal levels, after 1 year of treatment. Bone mineral density and bone biopsy indexes showed general improvement after calcifediol. In conclusion, calcifediol seems to act positively on the disorders of mineral metabolism in CAPD.