BACKGROUND: Vitamin D intoxication is associated with the mobilization of skeletal calcium. OBJECTIVE: To ascertain how the resolution of vitamin D intoxication affects bone density. DESIGN: Case series. SETTING: Referral service for metabolic bone disease in a tertiary care teaching hospital. PATIENTS: Four patients with osteoporosis who were each using several nonprescription dietary supplements and were found to have fasting hypercalciuria. INTERVENTION: Discontinuation of use of dietary supplements. MEASUREMENTS: Serial measurement of serum levels of 25-hydroxyvitamin D, ratio of fasting urinary calcium to creatinine, and bone mineral density for 3 years. RESULTS: Discontinuation of use of dietary supplements resulted in the normalization of serum levels of 25-hydroxyvitamin D, the normalization of the ratio of urinary calcium to creatinine, and a mean annual increase in bone mineral density (+/- SD) of 1.9% +/- 0.5%. CONCLUSIONS: Occult vitamin D intoxication was detected in patients who were using dietary supplements that contained an unadvertised high level of vitamin D. Resolution of vitamin D intoxication was associated with a rebound in bone mineral density.