The incidence rates of esophageal and gastric cardia adenocarcinoma (EGCA) have increased over recent years in several countries, and overweight/obesity has been suggested to play a major role in these trends. In fact, higher body mass index (BMI) has been positively associated with EGCA in several studies. We conducted a meta-analysis of case–control and cohort studies on the BMI and EGCA updated to March 2011. We estimated overall relative risks (RRs) and 95% confidence intervals (CI) for BMI between 25 and 30 and BMI ≥ 30 kg/m2, when compared with normo-weight subjects, using random-effects models. We identified 22 studies, including almost 8000 EGCA cases. The overall RR was 1.71 (95% CI 1.50–1.96) for BMI between 25 and 30, and was 2.34 (95% CI 1.95–2.81) for BMI ≥ 30 kg/m2. The continuous RR for an increment of 5 kg/m2 of BMI was 1.11 (95% CI 1.09–1.14). The association was stronger for esophageal adenocarcinoma (RR for BMI ≥ 30 kg/m2 = 2.73, 95% CI 2.16–3.46) than for gastric cardia adenocarcinoma (RR for BMI ≥ 30 kg/m2 = 1.93, 95% CI 1.52–2.45). No substantial differences emerged across strata of sex and geographic areas. Overweight and obesity are strongly related to EGCA, particularly to espophageal adenocarcinoma.