© 2019, Hellenic Society of Gastroenterology. All rights reserved. Background Pancreatitis is a potential major complication after endoscopic retrograde cholangiopancreatography (post-ERCP pancreatitis; PEP). Obesity has been associated with increased severity of acute pancreatitis. However, the correlation between obesity and PEP is controversial. Therefore, our study aimed to clarify the relationship between body mass index (BMI) and the incidence and severity of PEP. Methods A retrospective cohort study was conducted to elucidate the relationship between BMI and PEP in all patients who underwent ERCP in a tertiary referral center between January 2009 and October 2016. Patient characteristics and procedure details were collected. PEP was defined by consensus criteria. Multivariate logistic regression was used to determine the association between BMI and PEP. Results The analysis included 2236 patients whose BMI was recorded and had adequate follow up (921 with BMI≥30 kg/m2, 1315 with BMI<30 kg/m2). PEP was diagnosed in 107 4.8%) patients. PEP was seen in 49 obese patients (5.3%) and 58 non-obese patients (4.4%). In the univariate and multivariate analysis BMI≥30 g/m2 was not associated with PEP (odds ratio 1.2, 95%CI 0.8-1.8; P=0.32). A subgroup analysis of different BMI subcategories found that BMI was not associated with the incidence or severity of PEP. Conclusion In the largest study to date, neither obesity nor low body weight increased the incidence or severity of PEP.