BACKGROUND: Whether obesity and being overweight, defined by body mass index (BMI), increase hepatocellular carcinoma (HCC) has been less apparent in Asian populations. METHODS: Overall, 14,265,822 Korean adults who underwent routine health examinations during 2003–2006 were followed up for HCC. Multivariable-adjusted hazard ratios (HRs) associated with BMI were calculated. RESULTS: During 13.7 years (mean) of follow-up, 47,308 individuals developed HCC. HRs of HCC associated with BMIs of 25.0–26.4, 26.5–27.9, 28.0–29.4, 29.5–30.9 and ≥31 kg/m² compared to those for 23.5–24.9 kg/m² were 1.05, 1.20, 1.39, 1.59 and 2.13, respectively. For BMI