Deficiency of hypoxanthine phosphoribosyltransferase (HPRT) has a broad spectrum of clinical manifestations, from the complete enzyme defect, the Lesch-Nyhan syndrome with severe neurological deficiency to the partial defect associated only with uric acid overproduction and its consequences. We present a 5-year old boy with Lesch-Nyhan syndrome. He came to our hospital because of abdominal pain, vomiting and gross haematuria. At the age of 8 months he was categorized as a "cerebral palsy" patient due to involuntary movements and high degree of spastically and tonic spasms. He remained incapable of sitting or standing alone. The patient's brother and two uncles were also categorized as "cerebral palsy" cases and died at the age of 8-14 years. Clinical examination revealed hyperuricaemia and hyperuricosuria, radiolucent renal and urinary bladder stones. HPRT enzyme activity was totally absent, while adenine phosphoribosyl transferase activity was increased compared to control. The patient was treated with allopurinol, urinary alkalization, low-purine diet and adequate hydration while he was in hospital. However, his parents refused further treatment and follow-up. The most important issue is whether the healthy sisters of the patients are heterozygotes for HPRT deficiency. This DNA analysis is now in progress.