Incidence rates for liver cancer have increased 3-fold since the mid-1970s in the United States in parallel with increasing trends for obesity and type II diabetes mellitus. We conducted an analysis of baseline body mass index (BMI), waist circumference (WC), and type II diabetes mellitus with risk of liver cancer. The Liver Cancer Pooling Project maintains harmonized data from 1.57 million adults enrolled in 14 U.S.-based prospective studies. Cox regression estimated HRs and 95% confidence intervals (CI) adjusted for age, sex, study center, alcohol, smoking, race, and BMI (for WC and type II diabetes mellitus). Stratified analyses assessed whether the BMI-liver cancer associations differed by hepatitis sera-positivity in nested analyses for a subset of cases (n = 220) and controls (n = 547). After enrollment, 2,162 incident liver cancer diagnoses were identified. BMI, per 5 kg/m2, was associated with higher risks of liver cancer, more so for men (HR = 1.38; 95% CI, 1.30-1.46) than women (HR = 1.25; 95% CI, 1.17-1.35; Pinteraction = 0.02). WC, per 5 cm, was associated with higher risks of liver cancer, approximately equally by sex (overall, HR = 1.08; 95% CI, 1.04-1.13). Type II diabetes mellitus was associated with higher risk of liver cancer (HR = 2.61; 95% CI, 2.34-2.91). In stratified analyses, there was a null association between BMI and liver cancer risk for participants who were sera-positive for hepatitis. This study suggests that high BMI, high WC, and type II diabetes mellitus are associated with higher risks of liver cancer and that the association may differ by status of viral hepatitis infection.