Renal arteriovenous fistula is a rare clinical entity. Its presence may cause profound physiological aberrations; yet its recognition and correction may lead to dramatic alleviation of crippling cardiovascular disease. Twelve cases of renal arteriovenous fistula have been reported in the literature, and the present paper describes a thirteenth. This case demonstrates the problems associated with diagnosing the condition, the serious cardiovascular complications that may be encountered, and the dramatic improvement in cardiovascular status which may follow surgical correction. Report of a Case The patient, a 53-year-old white man, was admitted to the urological service of Roswell Park Memorial Institute with a three-week history of painless hematuria. An intravenous pyelogram done elsewhere was reported as showing a filling defect in the upper pole of the right kidney, suggesting the presence of a tumor in this area. The past history was not remarkable, except for long-standing hypertension and a nine-month period of