Xanthinuria is a rare cause of nephrolithiasis and is usually due to an inherited abnormality in purine metabolism. A 5-year 6-month-old boy was assessed for a history of recurrent episodes of renal colic. The child first presented with symptoms due to xanthine calculi at 1 month of age, the youngest presentation we were able to identify. Xanthine calculi, although rare, should be considered in the differential diagnosis of nephrolithiasis and ureterovesical junction obstruction in children. Xanthine calculi should also be considered when symptoms suggestive of urinary tract infection are present but the urine culture is negative, and when an orange-brown sediment is noted in the urine or similar coloured stains are found in the nappy.