Background: There is a scarcity of data regarding the radiation dose and associated risks to patients during ERCP. Dose area product (DAP) measurements can be used to estimate an effective dose (ED) to patients undergoing ERCP. This measure allows radiation risk associated with such procedures to be quantified. The aim of this study was to evaluate the ED to patients undergoing ERCP. Methods: A DAP meter was fitted to the x-ray tube before each ERCP. DAP reading (Gy-cm²), fluoroscopy time, average screening kVp, number of films, and kVp per film were recorded. Mean ED was estimated by using DAP readings and Monte Carlo computer software to model radiation exposure conditions. Results: Data were recorded on 20 subjects. Average DAP was 13.5 Gy-cm² (6.8-23.9) for diagnostic and 66.8 Gy-cm² (28.7-108.5) for therapeutic ERCP (p < 0.05). Average fluoroscopy time was 2.3 minutes (1.1-5.3) for diagnostic and 10.5 minutes (5.9-16.6) for therapeutic ERCP (p < 0.05). DAP showed a linear relationship with fluoroscopy time (R² = 0.928). Mean number of diagnostic and therapeutic films was 2.8 and 3.7, respectively. Fluoroscopic exposure represented 69% of the DAP for diagnostic ERCP and 90% of the DAP for therapeutic ERCP. Average ED was 3.1 mSv for diagnostic and 12.4 mSv for therapeutic ERCP. Conclusions: Therapeutic ERCP is associated with significantly higher radiation exposure than diagnostic ERCP. ED in therapeutic ERCP is a result largely of fluoroscopy time as opposed to number of films. (Gastrointest Endosc 2001;53:161-4.)