The information concerning the relationship of hypouricemia with urinary tract stones is limited. We investigated the incidence and types of hypouricemia, and also studied its relationship to urinary tract stones. Hypouricemia was detected in 3 out of 1520 outpatients (0.20%). The loading tests using pyrazinamide, probenecid and benzbromarone showed that uric acid absorption was impaired before tubular secretion in two cases and incomplete postsecretory reabsorption in one case. Complication of urinary tract stone was found in two cases. The composition of the stones was mixed calcium oxalate and uric acid. Hypouricemia should be recognized as one of the causes of kidney stone formation.