Right-lobe graft has been used most frequently for living donor liver transplantation in adult patients; however, some donors cannot donate their right lobe (according to the Healey and Scroy's terminology) because the remaining residual liver would be too small. A recent study suggested the possibility of right posterior segment graft in these donors. The purpose of this study was to evaluate the feasibility of right lobe or right posterior segment graft with a volumetric analysis. Liver volumetry by computed tomography was performed in 155 consecutive donors, and the volume of each liver segment was calculated. To confirm the reliability of volumetric examination, the estimated graft volume and the actual weight were compared. The average volume ratios of the left lateral segment, left medial segment, caudate lobe, right anterior segment, and right posterior segment were 17%, 14%, 2%, 37%, and 30%, respectively. In 39 donors (25%), the volume ratio of the right lobe was over 70%. Of these donors, 72% had a larger (difference in volume ratio greater than 5%) right posterior segment than left lobe with caudate lobe. The relationship between the estimated volume and actual weight was linear. The present results suggest that right lobectomy carries a potential risk and that the right posterior segment may be useful as an alternative graft from the point of donor's safety.