Symptomatic ulceration developed at a previous ileocolonic anastomosis in six children. In the neonatal period all patients had had necrotizing enterocolitis that required resection of the terminal ileum, ileocecal valve, and proximal portion of the colon. Gross or occult rectal bleeding, with or without pain and diarrhea, began 5 1/2 years after successful resection and ileocolonic anastomosis. The cause of the ulcers is unknown. They appear inflammatory, both grossly and histologically, but have been uniformly unresponsive to antiinflammatory medications, antibiotics, and immunosuppressive medication. Surgical revision of the anastomosis and ulcer resection in five patients have resulted in rapid recurrence in four. Thirteen similar cases have been reported in the English-language literature. We conclude that ulceration is a long-term complication of neonatal resection of the terminal ileum and ascending colon with ileocolonic anastomosis.