Background and Aims: The relative effects of obesity compared to alcohol on liver injury are uncertain. We examined their effects on alanine aminotransferase (ALT) and gamma glutamyltransferase (GGT) levels in a population-based cohort.Methods: Adult residents (2610: 1326 males, 1284 females) from Busselton, Australia, participated in a cross-sectional survey determining alcohol intake as determined by a validated questionnaire, anthropometric measurements and serum analysis. Alcohol consumption was classified as never, light (< 140 g/week), moderate (140-420 g/week) or heavy (> 420 g/week).Results: The majority of subjects were either overweight (41%) or obese (17%). A minority of subjects were moderate (25%) or heavy drinkers (4%). Body mass index (BMI) and waist circumference were strongly associated with ALT and GGT (P < 0.0001 for all tests). Alcohol consumption was modestly associated with ALT in females (P = 0.01) but not in males (P = 0.9). In contrast, GGT was significantly associated with alcohol in both genders (P < 0.0005). The risk of an elevated ALT was seven-fold higher with obesity but only two-fold higher with moderate or heavy alcohol use. Obesity accounted for half of all elevated ALT levels in the cohort, whereas alcohol excess was responsible for less than 10%. No synergistic effect was observed between BMI or waist circumference and alcohol on ALT or GGT (P > 0.2 for all tests).Conclusions: Excess weight is more common than excessive alcohol consumption in the community and confers a greater risk of elevated aminotransaminase levels.