The respective volumes of hepatic tumors and nontumorous parenchyma of 50 patients requiring hepatectomy of more than one segment of Healey for tumor removal were measured using computed tomography (Vol-CT). The volume estimated by Vol-CT was found to correlate with the real weight resected (P < .0001) with a mean absolute error of 64.9 mL. The ratio of the nontumorous parenchymal volume of the resected liver to that of the whole liver (R2) in 15 patients who underwent right or extended right hepatic lobectomy was 43% +/- 15%. Eight of 15 patients with R2s < 60% underwent the procedures without right portal vein embolization (PE). The other seven with R2s exceeding 60% or an indocyanine green retention rate after 15 minutes (ICG15) of 10% to 20% underwent PE: in six of seven, the nontumorous parenchyma of the right hepatic lobe became atrophic and in all seven, the volume of the remaining left hepatic lobe increased with a decrease in the mean R2 from 62% +/- 14% to 55% +/- 8% (P = .0006). In the remaining 35 who underwent other hepatectomy procedures, R2s also remained <60%. Overall, at surgery, in 27 with normal liver function (ICG15 < 10%), R2s exceeded 60% in one, remained at 50% to 60% in five, and <50% in 21, whereas 23 patients except for one with an ICG15 exceeding 10%, had R2s of <50%. The postoperative serum total bilirubin levels in 84% of the patients remained within the normal range and there was no surgery-related mortality. In conclusion, 1) Vol-CT can accurately assess the extent of liver resection, 2) individuals with normal liver function can undergo resection of up to 60% of the nontumorous parenchyma without the need for PE, and 3) PE can be used to reduce the size of the resected tissue and increase the volume of the remnant liver to approximate the target limits in individuals with large tumors or minimally abnormal liver function.