OBJECTIVE To measure the renal parenchymal volume (RPV) before and after unilateral nephrectomy and investigate the relationship between the RPV and single kidney glomerular filtration rate (GFR). METHODS From November 2003 to August 2009, 183 patients who had undergone unilateral nephrectomy were enrolled in the present study. All patients had undergone preoperative technetium-99m dimercaptosuccinic acid renal scintigraphy. Contrast-enhanced computed tomography was performed before and 6 months after surgery. RPV was calculated as the normally functioning tissue, excluding tumors or nonenhanced areas, using a 3-dimensional image reconstruction program. RESULTS The mean split GFR of the remaining kidney increased by 21.2%, from 41.6 to 49.5 mL/min/1.73 m(2) at 6 months after nephrectomy. The mean RPV of the remaining kidney increased by 9.3%, from 164.2 to 178.8 cm(3) after nephrectomy. The preoperative relative RPV of the remaining kidney was 58.8% (range 37.2%-97.9%) and the technetium-99m dimercaptosuccinic acid uptake was 62.2% (range 39.6%-100%), indicating a significant linear correlation (R = 0.865, P <.001). RPV correlated well with the single kidney GFR and patient age, both preoperatively and postoperatively. The postoperative GFR could be predicted by combining the preoperative factors. Multivariate regression analysis revealed that the RPV was positively associated with the single kidney GFR and negatively associated with patient age. CONCLUSIONS The differential renal function correlated well with the RPV and can be estimated by calculating the RPV. Even without using renal scintigraphy, the postoperative GFR can be predicted using our established formula.