Five cases of primary linitis plastica of the rectum are presented. The clinical, radiologic, and pathologic features of the disease are described with emphasis on the difficulty in establishing a correct preoperative diagnosis. Because the histologic features of primary and secondary linitis plastica are indistinguishable and because secondary involvement is twice as common as primary, it is mandatory that other sites of origin are excluded and that both the proximal and distal margins of the resected area be free of tumor.