Inflammatory myofibroblastic tumor is a rare benign condition of unknown etiology, and it may simulate malignancy. It is composed of myofibroblast, plasma cells and histiocytes and is found in lung, the liver, orbit, skin, mesentery, retroperitoneum and maxillary sinus. We report a case of inflammatory myofibroblastic tumor of perineal subcutaneous fat in a 35-year-old woman who complained of a palpable mass. Ultrasonography revealed a well-marginated lobulated hypoechoic lesion with peripheral poorly-defined hyperechoic strands in the subcutaneous fat of the right perineum. The lesion demonstrated low signal intensity on T1-weighted images and of heterogenous high signal intensity on T2-weighted images, compared with surrounding muscle. After intravenous injection of gadolinium, it showed clear homogeneous enhancement but poorly-defined adjacent strands. The final histologic diagnosis was inflammatory myofibroblastic tumor.