No optimal tacrolimus dosage regimen suitable for clinical use in liver transplant recipients has yet been established. The purpose of this study was to determine the factors affecting the optimal dosage and pharmacokinetics of tacrolimus in living donor liver transplantation, and a nomogram for optimal tacrolimus dosage in the immediate postoperative period for recipients with small-for-size grafts was constructed. Twenty-four liver transplant patients (nine males and 15 females) and 24 donors (10 males and 14 females) were enrolled in this study. Two studies were performed. In study 1, the effect of the actual ratio of graft volume to standard liver volume (GV/SV ratio) on the elimination half-life (T1/2) of tacrolimus in the immediate postoperative period was analysed, and a nomogram for estimating the optimal oral dose of tacrolimus required to reach a target concentration was established. In study 2, the effect of donor age on the recovery of hepatic function with ability of the graft to eliminate tacrolimus was analysed. In the immediate postoperative period, T1/2 of tacrolimus showed great variability between patients, with values ranging from 16.3 to 110.9 h. Graft size (GV/SV ratio) is important and could influence intraindividual variations in the optimal dosage and T1/2 of tacrolimus. The recovered T1/2 ratio (T1/2 ratio=T1/2 1-10 d/T1/2 30-40 d), this ratio being related to the recovery of hepatic function with ability of the graft to eliminate tacrolimus, showed great variability between patients, with values ranging from 1.08 to 4.21 (mean+/-SD, 1.95+/-0.81). Age of the donor is a major factor affecting the recovered ratio of the graft to metabolize tacrolimus. The nomogram that we have constructed, based on graft size (GV/SV ratio), will easily provide optimal dose for each patient with small-for-size graft in the early postoperative period.