The perineum is defined as the region of body below the pelvic diaphragm that lies within the boundaries of the pelvic outlet. It is the region which is home to pathologic conditions which include primary tumors, neoplasms of adjacent organs with secondary invo l vement, congenital or acquired cystic lesions and inflammatory lesions. In this article, we describe CT and MR imaging anatomy and various pathologic processes that affect this anatomic region, with a brief discussion. Emphasis is give n to imaging features that help to characterize specific lesions.