Lesch-Nyhan syndrome is a rare X-linked recessive disorder of purine metabolism 
associated with a virtually complete deficiency of the enzyme 
hypoxanthine-guanine phosphoribosyl-transferase (HPRT). The disease is 
characterized by hyperuricemia, self-multilation, choreoathetosis, spasticity, 
and mental retardation. The abnormalities of purine metabolism are present at 
birth and may lead to uric acid crystalluria and stone formation early in life. 
Radiographic findings described in Lesch-Nyhan syndrome include faintly 
radio-opaque stones on abdominal radiographs or, if renal disease is present, 
small kidneys with poor function on intravenous urogram. Radiolucent stones are 
usually composed of uric acid; however, several cases of xanthine and 
hypoxanthine-containing calculi in Lesch-Nyhan patients receiving allopurinl 
therapy have also been described. Oxypurine is the collective name for the 
compounds hypoxanthine, xanthine, and uric acid, and all may be radiolucent. We 
report a case of Lesch-Nyhan syndrome with presumed renal parenchymal oxypurine 
deposition demonstrated readily by ultrasonography but not detected on standard 
radiographs or intravenous urograms.