Unilateral nephrectomy causes immediate changes in renal plasma flow, glomerular filtration, and fractional sodium excretion of the remnant kidney. The present study reviews some aspects of reports published elsewhere relative to renal function adaptation after unilateral nephrectomy and presents the observed changes in creatinine clearance, fractional sodium excretion at 6, 30 and 90 days following removal of kidneys with chronic urologic disease and poor function, in a total of 20 patients. The results obtained show a gradual increase of creatinine clearance in most of the patients, although this increase was not statistically significant. On the other hand, fractional sodium excretion rose significantly at 30 and 90 days after nephrectomy. These findings can be interpreted in the following way: among the regulatory mechanisms, at 6 days postnephrectomy there is a predominance of the effects of increased CINa load to the distal tubule with activation of the renin-angiotensin system, as well as those produced by sympathetic efferents characteristic of the immediate postoperative period. However, at 30 and 90 days, the effects that seem to predominate are due to the expansion of the volume of extracellular fluid. Data obtained at 90 days indicate that balance seems to become stable.