Adenovirus-induced haemorrhagic cystitis has been reported chiefly in bone marrow or kidney transplant recipients. We report here on an HIV-positive patient treated for a Burkitt's lymphoma who developed gross haematuria associated with fever and burning urination. Usual causes of haematuria were ruled out: lithiasis, urinary tract lesions, glomerulonephritis, mycobacterium and schistosoma infections, and drug toxicity. Adenovirus was detected by cellular cultures and BK/JC virus DNA sequences were detected using a polymerase chain reaction method. Because BK/JC virus shedding is very common (75%) in HIV patients receiving chemotherapy, our data strongly suggest that adenovirus was responsible for the haemorrhagic cystitis in our patient. In conclusion, adenovirus should be considered as a potential cause of haemorrhagic cystitis in AIDS patients whose immunosuppression is aggravated by cytotoxic drugs.