A detailed description is given of the principles and surgical technique for extensive resection of the sacrum, including an adjacent part of each ilium, for radical removal of tumor. Two levels of sacral amputation are discussed: between S1 and S2 (through the canals of the S1 nerves) and through S1 (above the canals of the S1 nerves), with or without inclusion of the rectum in the specimen. The former level permits the preservation of the S1 nerves; the latter does not. Important pathoanatomic facts are discussed. The effects of these operations on the urogenital and anorectal function and on the stability of the pelvic girdle are briefly reviewed. Five illustrative cases are reported with comments on the results.