AIMS--To investigate a female patient with a tumour mass of the terminal ileum, to define the nature of the tumour, and to correlate its morphology and behaviour with similar types of tumours of the large intestine and stomach. METHODS--Tissues obtained at colonoscopy, from hemicolectomy specimens, and from liver and peritoneal biopsy specimens were studied macroscopically, microscopically, histochemically, and immunohistochemically for epithelial membrane antigen (EMA), carcinoembryonic antigen (CEA), neuron specific enolase (NSE), and S100 protein. RESULTS--Macroscopic examination showed a tumour of the terminal ileum protruding into the caecum. Microscopically the tumour showed two components, one adenoma with moderate dysplasia and the other carcinoid tumour. The adenomatous component stained positively for EMA and CEA and negatively for NSE. The carcinoid component stained positively for NSE and negatively for EMA and CEA. Histochemically the carcinoid area was argyrophil positive and argentaffin negative. Only the carcinoid had metastasised, to the liver, peritoneum, and the lymph nodes, at the time of diagnosis. CONCLUSION--The morphological, histochemical, and immunohistochemical findings confirm the diagnosis of a composite adenoma-carcinoid tumour of the terminal ileum.