A 5-year-old boy was found to have severe rickets in association with hyperpigmented, linear, verrucous, epidermal tumors, typical of the epidermal nevas syndrome. Normocalcemia (9.6 mg/dl), hypophosphatemia (2.0 mg/dl), elevated serun alkaline phosphatase concentration (313 IU), decreased renal tubular reabsorption of phosphorus (35%), radiologic evidence of rickets, and lack of response to usual therapeutic doses of vitamin D suggested hypophosphatemic vitamin D-resistant rickets. Therapy with vitamin D in doses to 750,000 IU and oral phosphate, 2.0 gm/day, failed to induce healing of the rickets. A subtotal parathyroidectomy performed when the patient was 9 years old was also without effect. When he was 12 years old several fibroangiomas on the face and left lower limb were excised. Within three months all biochemical abnormalities resolved and radiologic evidence of healing was observed. A portion of excised tissue was homogenized and injection of the supermate into a 6-week-old puppy induced excessive phosphaturia. The data suggest that the rickets was induced by a phosphaturic substance extractable from the tumors.