Medical records of patients having unilateral nephrectomies done between 1953 and 1978 at a university hospital were reviewed after 5 to 30 years of follow-up to determine if this procedure causes insidious renal insufficiency. Forty patients (selected from 571) ranging in age from 20 to 72 years met the following criteria for inclusion in the study: subject over 20 years of age at nephrectomy; initial serum creatinine concentration less than 1.6 mg/dL; normal arterial blood pressure (less than 150/90 mm Hg); absence of risk factors for chronic renal disease, eg, systemic lupus erythematosis, diabetes mellitus, chronic glomerulonephritis; an initial and a follow-up serum creatinine level; at least 5 years of follow-up. After a mean follow-up of 11.8 years, paired analysis of changes in serum creatinine concentrations showed insignificant differences between pre- and post-nephrectomy levels (0.19 +/- 0.11 mg/dL +/- SEM). Only one patient had a post-nephrectomy serum creatinine level above 2.0 mg/dL. Six patients (four women, two men) developed hypertension (15%) after uninephrectomy, an incidence of hypertension not greater than that found in the population at large. We conclude that uninephrectomy at ages older than 20 years does not lead to renal insufficiency or hypertension in adult patients with normal prenephrectomy serum creatinine and blood pressure levels.