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Background: Autoimmune pancreatitis (AIP) is a chronic inflammatory condition characterized by IgG4-positive plasma cells. Recent evidence suggests that it is a systemic disease affecting various organs. Tubulointerstitial nephritis has been reported in association with AIP. Purpose: To investigate the incidence and types of renal involvement in patients with AIP. Material and Methods: Eighteen patients with no history of renal disease and a diagnosis of AIP (on the basis of histopathologic findings or a combination of characteristic imaging features, increased serum IgG4 levels, and response to steroid treatment) were included. All patients underwent computed tomography (CT) imaging and follow-up ranged from 6 months to 2 years. CT images were reviewed for the presence of renal lesions. Results: Seven patients had renal involvement (38.8%). None of the lesions was visible on non-contrast-enhanced CT scan. Parenchymal lesions appeared as multiple nodules showing decreased enhancement (four cases). Pyelonephritis, lymphoma, and metastases were considered in the differential diagnosis. An ill-defined low-attenuation mass-like lesion was found in one patient, while diffuse thickening of the renal pelvis wall was evident in the last two cases. Renal lesions regressed in all patients after steroid treatment, the larger one leaving a fibrous cortical scar. Conclusion: Different types of renal lesions in patients with AIP are relatively common, appearing as multiple nodules with decreased enhancement. These findings support the proposed concept of an IgG4-related systemic disease. Autoimmune disease should be suspected in cases of renal involvement in association with pancreatic focal or diffuse enlargement. [ABSTRACT FROM AUTHOR]