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To evaluate the effectiveness of magnetic resonance imaging (MRI) in predicting the location, type of ductal involvement, and malignant transformation of intraductal papillary mucinous (IPM) pancreatic tumors made in a preoperative routine exam.A total of 24 patients with histologic confirmation of IPM tumor (IPMT) were included in this study. The MR images obtained in operation patients were retrospectively assessed. Two radiologists who were unaware of the initial interpretations of the images independently analyzed the MRI studies and characterized the type of lesions, location, and signs of malignant transformation. Interobserver agreement was determined with weighted kappa statistics. After consensus of both radiologists, the observer performances for the MRI interpretations were compared with surgical and histologic results using weighted kappa statistics and Fisher test.At macroscopic examination, lesions were of combined type in 17 cases and of branch duct type in seven cases. At histologic analysis, three cases were classified as benign, three as borderline tumors, and 18 as carcinomas (eight in situ, 10 invasive). The lesions were located mainly in the head or uncinate process (N = 16) or were diffuse or multifocal (N = 2). Excellent agreement was found between the interpreters (0.90) in the evaluation of ductal involvement, good in the evaluation of lesion location (0.80) and in the diagnosis of malignant transformation (0.74). The correlation between MRI and histopathologic results was excellent in the evaluation of ductal involvement (0.90, sensitivity = 100%, specificity = 94%) and moderate in the evaluation of lesion location (0.57, sensitivity = 87%, specificity = 56%) and in the diagnosis of malignant transformation (0.60, sensitivity = 83%, specificity = 83%).MRI is an effective method of characterizing IPMT in preoperative practice. The predictive sign of IPM pancreatic tumor malignancy at MRI included only the presence of solid mass or mural nodules. J. Magn. Reson. Imaging 2005;21:237–244. © 2005 Wiley-Liss, Inc.