The value of CT in the preoperative management of tumors of the sacrum is demonstrated. Essential informations for treatment planning are: involved sacral segment, infiltration of sacral foramina and nerve roots, involvement of the sacroiliac joints, ingression of the lumbar spine, infiltration of the pelvic organs and vessels, sciatic nerve and the dorsal soft tissues. In order to prove the competence of the CT in answering these questions we evaluated the CT-examinations of 30 pat. with 14 primary tumors, 9 metastatic tumors and 7 tumors involving secondary the sacrum. The CT findings were correlated with clinical symptoms and surgical reports in 11 pat., with clinical symptoms alone in 19 pat. There was good correlation in the criterias: location and number of involved segments (8/11, 17/19), infiltr. of SI-joints (11/11), infiltr. of lumbar spine (9/11, 18/19), and infiltr. of pelvic organs (10/11), worse correlation in the criterias: nerve root-involvement (2/11, 3/19), and sciatic nerve-infiltr. (7/11, 15/19). Our conclusions are that CT gives helpful preoperative informations deciding about extent of surgical procedure, and surgical approach. The major problem, however, consist in diagnosis of nerve root and sciatic nerve involvement, therefore in poor prediction of postoperative conservation of neural functions. The knowledge of CT-anatomy of sacrum- and important condition for correct segment-location of the tumor is refreshed by outlines of characteristic segmental CT-sections of the sacrum.