The incidence of oesophageal adenocarcinoma (EADC) is rapidly increasing in Western countries and obesity is thought to be a major risk factor. We examined the association between BMI and EADC, gastric cardia adenocarcinoma and gastric non-cardia adenocarcinoma in a cohort of approximately 500,000 people in the United States (US). We used Cox proportional hazards regression to estimate hazard ratios (HR) and 95% confidence intervals (CI) with control for many potential confounders. We found that compared to people with a BMI of 18.5-25kg/m2, a BMI > or = 35 was associated with significantly increased risk of EADC, HR (95% CI)=2.27 (1.44-3.59) and gastric cardia adenocarcinoma 2.46 (1.60-3.80), but not gastric non-cardia adenocarcinoma 0.84 (0.50-1.42). Using non-linear models, we found that higher BMI was associated with increased risk of EADC even within the normal BMI. Increased adiposity was associated with higher risk of EADC even within the normal weight range.