['To evaluate the influence of body mass index (BMI) on postoperative death in patients undergoing surgery for HCC.', 'Three hundred forty-two patients were enrolled, and divided into three groups: Group A, BMI <22.5; Group B, BMI ≥22.5 to <25; Group C, BMI ≥25. Univariate and multivariate analyses of postoperative death were performed to compare BMI with clinical factors. Kaplan-Meier analysis and log rank test were used to compare such outcome in Groups A, B, and C.', 'Kaplan-Meier analysis and log rank test revealed that Group A had a higher rate of postoperative death than Group B or C (P = 0.010). Univariate and multivariate analyses selected being underweight (Group B, C/Group A) (odds ratio, 1.829; 95% C.I., 1.091-3.068; P = 0.022) as one of the factors predictive of postoperative death, together with aspartate aminotransferase level (P = 0.042) and HCC growth pattern (P = 0.032).'] Do underweight patients show an increased rate of postoperative death after surgery for hepatocellular carcinoma?