High BMI is associated with increased risk of future severe liver disease, including hepatocellular carcinoma (HCC). However, high BMI predisposes for type 2 diabetes mellitus (T2DM), which is also associated with HCC, but whether the long-term risk of developing severe liver disease is further increased by T2DM was unknown. Now, in a population-based cohort study of 1.2 million men, data on the development of T2DM and liver disease were used to estimate hazard ratios for liver disease mortality and HCC incidence across BMI categories. After a mean follow-up period of 28.5 years, 5,281 cases of severe liver disease and 251 cases of HCC were identified. High BMI in late adolescence was associated with future severe liver disease and HCC, but development of T2DM was associated with an increased risk across all BMI categories, suggesting that men who develop T2DM should be screened for liver disease.