Sufficiently detailed information on donor safety and the liver regeneration process following right-lobe living donation has been unavailable, so we evaluated donor outcome and liver regeneration in 13 males and 14 females (39.0 +/- 14.8 years old) who provided 27 right-lobe grafts without the middle hepatic vein. Preoperative total liver volume (TLV), graft volume, and postoperative changes in residual liver volume (RLV) were measured by volumetric computed tomography. Histological steatosis of the liver was graded as none, minimal (< or =10%), and mild (11-30%). The median follow-up period was 337 days. Estimated graft volume and actual graft weight were linearly correlated (Y = 177.85 + 0.795X, R(2) = 0.812, P < 0.0001). Graft-to-recipient weight ratio was 1.08 +/- 0.19%. Four donors had postoperative complications, but they resolved in response to conservative treatment. Postoperative hospital stay was 15.2 +/- 5.5 days. Peak liver enzyme values were significantly higher in donors with mild steatosis (n = 7) than without steatosis (n = 16) (P < 0.05). Donor RLV was 40.8 +/- 6.6% of original TLV at surgery, 79.8 +/- 12.0% by 6 months, and 97.2 +/- 10.8% by 12 months. At 3 months the liver of the older donors (> or =50 years) had grown significantly more slowly than in younger donors (70.4 +/- 9.2% vs. 79.3 +/- 9.6%, P = 0.0391). In conclusion, right hepatectomy without middle hepatic vein of living donors is a safe procedure with acceptable morbidity, and the residual liver regenerated to its preoperative size by 1 year. However, meticulous care should be taken in donors with liver steatosis and aged donors.