1. Of 104 patients with renal calculi, 42% gave a history of previous self-medication with multivitamin preparations containing vitamin D, compared with 37% of a control group of fifty-one patients without renal calculi. This difference is not significant.
2. The mean supplemental daily intake of vitamin D and the annual intake were significantly higher in the patients with renal calculi than in the control group.
3. The highest mean supplemental intake of vitamin D occurred among those patients in whom no metabolic or other cause for renal stone formation could be found.
4. The first calculi presented within 2 years of the period of self-medication in twenty-four of thirty patients who had not previously suffered from renal stones.
5. The results suggest that self-administration of vitamin D should be included among the aetiological factors promoting the formation of renal calculi.