About 1000 patients mostly with rectal carcinomas but also with hematomas, abscesses and soft tissue tumors received CT-examinations of the posterior compartment of the pelvis before and after surgical treatment and radiation therapy. The morphology of the perirectal space is demonstrated under normal and pathologic conditions and can be compared with the current anatomical knowledge. Special attention has been focussed on the site of the so called "Hüllfaszien" or "Grenzlamellen" of the rectum and the division of the perirectal space. Nomenclature and description of the perirectal fasciae and spaces are somewhat controversial. Therefore misinterpretations of pathologic CT-findings are not uncommon.