Dysuria, uric acid crystalluria and hyperuricosuria developed in a child with cystic fibrosis and normal serum uric acid. Hyperuricosuria in this patient and two other children was directly related to ingestion of large amounts of pancreatic extract. In these three children, reducing pancreatic extract dosage by 85 percent lowered their purine intake by 307, 225, and 148 mg, respectively; urinary uric acid excretion decreased by 245, 239, and 158 mg. Overmedication resulted from parents' decisions to increase enzyme dosages. In our cystic fibrosis clinic, 15 of 32 patients screened at random were taking higher than the prescribed dose of pancreatic enzymes, and 14 of these 15 children were hyperuricosuric. On the basis of this information, we suggest that the minimal effective dose of pancreatic extract should be determined and adhered to for each child with cystic fibrosis to avoid potential renal injury from hyperuricosuria.