BACKGROUND: Data on the association of Helicobacter pylori infection and BMI are conflicting. The fact that both H. pylori infection and BMI are associated with low socioeconomic status (SES) makes this relationship difficult to characterize. MATERIALS AND METHODS: We aimed to evaluate the association between BMI and H. pylori infection after adjusting for multiple covariates. We analyzed a cohort of 235 107 individuals aged 18 years or older, who performed a C urease breath test (C-UBT), from 2007 to 2014. Data on BMI, age, sex, SES, ethnicity, and medications were extracted from a nationwide population-based database. BMIs were classified according to the WHO recommendations: underweight (<18.5 kg/m), normal weight (18.5-24.9 kg/m), overweight (25-29.9 kg/m), obese class I (30-34.9 kg/m), and obese class II or more (>35 kg/m). STUDY RESULTS: The positivity rate for H. pylori among underweight, normal weight, overweight, and obese class I and class II or more was 55.6, 58.5, 63.0, 64.5, and 65.5%, respectively (P<0.001, Plinear trend 0.007). The association between BMI and H. pylori infection was significant across all SES, sex, ethnicity, and age categories. After adjusting for age, sex, ethnicity, and SES, being overweight and obese class I and class II or more were associated significantly with H. pylori positivity: odds ratio 1.13 [95% confidence interval (CI): 1.11-1.15], 1.14 (95% CI: 1.11-1.17), and 1.15 (95% CI: 1.11-1.19), respectively, P value less than 0.001 for all. CONCLUSION: Among individuals who were referred to a C-UBT by primary care physician, after adjusting for multiple covariates including SES, we found a positive association between H. pylori infection and an increased BMI.