A 36-year-old woman developed neutropenia following chemotherapy for inoperable carcinoma of the cervix. She suffered acute abdominal pain, nausea, vomiting, and peritonitis of rapid onset. The right hemicolon and 15 cm of terminal ileum were resected at laparotomy and this showed marked edema of the cecum and ileo-cecal valve associated with superficial ulceration of the valve. There was necrosis of submucosal tissues and the muscle wall which contained a large number of Gram-positive bacilli. These showed positive membrane immunofluorescence with specific anti-Clostridium septicum antisera. We identify a case of enterocolitis due to Clostridium septicum infection. This is associated with neutropenia and is often fatal due to the rapid course of and failure to recognize the infection.