OBJECTIVES: Intraductal papillary mucinous neoplasms (IPMNs) and pancreatic intraepithelial neoplasia (PanIN) are both precancerous lesions. Papillary mucinous neoplasms have been described in patients with IPMN, but their relationship is still poorly understood. The aims of this study were to look for PanIN lesions in patients operated on for IPMN and to search for correlations between endoscopic ultrasonography(EUS) features and pathologic findings. METHODS: Endoscopic ultrasonography was preoperatively performed in all patients with IPMN consecutively operated on in our center. Endoscopic ultrasonography features were prospectively compared with pathologic data from surgical specimen. RESULTS: Forty patients underwent resection for benign (52.5%) or malignant (47.5%) IPMN. Pancreatic intraepithelial neoplasia lesions were observed in 78% of cases (PanIN-3 in 19% of patients). PanIN-3 lesions were observed in 11% and 26% of patients with benign and malignant IPMN, respectively. Endoscopic ultrasonography changes(microcysts and/or hyperechoic foci) corresponded to PanIN lesions in 83% of cases. Endoscopic ultrasonography detected 69% of patients with PanIN lesions and 57% of those with panIN-3 lesions. CONCLUSIONS: Pancreatic intraepithelial neoplasia lesions are very frequently associated with IPMN, and 19% of patients with IPMN had PanIN-3 lesions. In two thirds of patients, EUS can detect minimal changes in the pancreas corresponding to PanIN lesions.