The clinical records from 507 adult patients surviving open-heart operations were reviewed to determine the incidence of renal dysfunction. Three hundred nine patients (61%) were considered to have maintained normal renal function throughout the postoperative period compared to 198 patients who developed a blood urea nitrogen (BUN) level of greater than 50 mg/100 ml or a serum creatinine level of greater than 2.0 mg/100 ml. The mortality in the former group was only 1.6% compared to 30.3% in the patients having abnormal renal function. Age and the mean preoperative BUN and creatinine values were substantially greater in the "abnormal" patients than in the "normal" patients. Although a cause and effect relationship between renal dysfunction and mortality cannot be made on the basis of the present study, the data suggest the prevalence of renal failure in the postoperative period and the potentially serious nature of this complication.