We describe a case of inflammatory pseudotumor involving the anal sphincter complex, and its ultrasonographyand MR imaging features. Transperineal ultrasonography showed a well-marginated ovoid low echoic lesionintermingled with sparse echogenic foci within the right anal sphincter complex. The lesion was of intermediatesignal intensity on T1-weighted images and of heterogeneous hyperintensity on T2-weighted, compared tosurrounding muscle. After the infusion of gadolinium, the le-sion showed heterogeneous enhancement, with amultifocal non-enhanced center. T 2 - weighted endorectal MR images were more accurate in depicting the lesion andanal sphincter complex, and the patient underwent surgical resection. The final histo-logic diagnosis wasinflammatory myofibroblastic tumor.