The association between invasive Clostridium septicum infection and colorectal carcinoma is examined by the presentation of three cases and a review of the literature. In the first two cases the patients presented with nontraumatic metastatic clostridial gas gangrene. In the third case a patient with chemotherapy-induced myelosuppression from concomitant multiple myeloma had a necrotizing transmural infection of the right colon. The apparent portal of entry of Clostridium septicum was an occult carcinoma of the ascending colon. The increasing evidence for a strong link between this organism and some cases of neutropenic enterocolitis is reviewed.