The extent of donor hepatectomy may affect splenic hypertrophy and platelet count. The subjects were 50 live liver donors. The ratio of the graft weight to total liver volume (GW/TLV) and the splenic hypertrophy ratio, expressed as the splenic volume one month after surgery divided by that before surgery, were calculated. The platelet count one month after surgery was divided by that before surgery to determine the rate of the platelet count decrease. The correlation of GW/TLV to the splenic hypertrophy ratio and the rate of the platelet count decrease were examined. The median (range) GW/TLV was 54 (28-71)%. The splenic hypertrophy ratio and the rate of the platelet count decrease was 133 (99-191)% and 92 (71-129)%, respectively. GW/TLV positively correlated with the splenic hypertrophy ratio (Spearman's correlation coefficient (r(s)) = 0.448, p = 0.001), and negatively correlated with the rate of the platelet count decrease (r(s) = -0.471, p < 0.001). Multivariate analysis revealed that GW/TLV influenced the splenic hypertrophy ratio [adjusted odds ratio (OR), 12.0; 95% confidence interval (CI), 1.32-9.04; p = 0.01] and the ratio of the platelet count decrease (adjusted OR, 11.6; 95% CI, 1.40-8.33; p = 0.01). Larger graft procurement might place living liver donors at higher risk for post-operative thrombocytopenia.