Background: Morbidity remains a common problem following hepatic resection. The aim of this study was to investigate the association between preoperative body mass index (BMI) and morbidity in patients undergoing liver resection for hepatocellular carcinoma (HCC). Methods: Patients were divided into three groups according to preoperative BMI: low-BMI (<= 18.4 kg/ m(2)), normal-BMI (18.5-24.9 kg/m(2)) and high-BMI (>= 25.0 kg/m(2)). Baseline characteristics, operative variables, postoperative 30-day mortality and morbidity were compared. Univariable and multivariable analyses were performed to identify independent risk factors associated with postoperative morbidity. Results: Among 1324 patients, 108 (8.2%), 733 (55.4%), and 483 (36.5%) were low-BMI, normal-BMI, and high-BMI, respectively. There were no differences in postoperative 30-day mortality among patients based on BMI (P = 0.199). Postoperative 30-day morbidity was, however, higher in low-BMI and high-BMI patients versus patients with a normal-BMI (33.3% and 32.1% vs. 22.9%, P = 0.018 and P < 0.001, respectively). Following multivariable analysis low-BMI and high-BMI remained independently associated with an increased risk of postoperative morbidity (OR: 1.701, 95%CI: 1.060-2.729, P = 0.028, and OR: 1.491, 95%CI: 1.131-1.966, P = 0.005, respectively). Similar results were noted in the incidence of postoperative 30-day surgical site infection (SSI). Conclusion: Compared with normal-BMI patients, low-BMI and high-BMI patients had higher postoperative morbidity, including a higher incidence of SSI after liver resection for HCC.