Hypercalcemia is a potential dosage-related adverse effect of 13-cis-retinoic acid in patients with neuroblastoma. Severe hypercalcemia requiring dosage reduction has been reported in children receiving 13-cis-retinoic acid 200 mg/m2/day and in those with concurrent renal impairment receiving 160 mg/m2/day. A 12-year-old girl without renal dysfunction, diagnosed with neuroblastoma, developed severe hypercalcemia requiring several hospitalizations while receiving 13-cis-retinoic acid 160 mg/m2/day. Her hypercalcemia resolved with hydration, diuretic therapy, and temporary discontinuation of 13-cis-retinoic acid. Despite a 50% dosage reduction to 80 mg/m2/day, severe hypercalcemia recurred with the next treatment cycle. Further treatment with 13-cis-retinoic acid was made tolerable by shortening the duration of the remaining cycles. Serum calcium levels should be monitored in patients with neuroblastoma who receive 13-cis-retinoic acid.