BACKGROUND The association of multisystem pathologic conditions and epidermal nevi, known as the epidermal nevus syndrome, includes disorders of bone, central nervous system, eye, kidney, vasculature, body symmetry, and skin. Rarely, vitamin D-resistant rickets has been observed in association with this syndrome. Precocious puberty is another rare finding associated with epidermal nevus syndrome, having been observed in 3 patients. METHODS A female infant with an extensive epidermal nevus, hypophosphatemia, and precocious puberty is described. Despite medical therapy, the patient's phosphate levels continued to be very low (0.87-0.97 mmol/L), establishing the diagnosis of hypophosphatemic vitamin D-resistant rickets. At 21 months of age, areas of the nevus were excised. Laboratory values obtained shortly after the operation showed a significant, but transient, improvement in the serum phosphate level. After a second excision, maintenance of her serum phosphate level in the range of 1.29 to 1.61 mmol/L was possible. CONCLUSIONS There is evidence that epidermal nevi produce a potent phosphaturic factor. We hypothesize that limited excision debulked the nevus sufficiently to allow medical management of the hypophosphatemia. Surgical intervention should be considered for patients affected with vitamin D-resistant rickets with epidermal nevi. The cause of the precocious puberty is unknown. It may be hypothesized that the nevus released a factor that induced puberty.