AbstractThirty‐one cases of carcinoma of the ampulla of Vater and duodenum have been classified on the basis of pathological criteria.Two types of tumour were discernible. Nine were polypoid papillary adenocarcinomas occurring at the ampulla of Vater; 19 were adenocarcinomas without a papillary pattern, of which 4 were duodenal tumours and 15 were ampullary. There were 3 ampullary tumours of mixed type. The carcinomas without a papillary structure were more invasive, more often associated with abdominal pain, more frequently misdiagnosed, and were associated with a higher mortality‐rate.The data were insufficient to draw firm conclusions as to the prognosis but the clinical behaviour was related to the pathology of the tumours.Lesions in the ampullary region were associated with jaundice which was often intermittent. Lesions outside the ampullary area presented early with vomiting of pyloric type but without jaundice.The importance of a high index of suspicion in dealing with these lesions and the value of barium‐meal examinations are emphasized.It is noted that pancreaticoduodenectomy for ampullary carcinoma has a mortality of less than 25 per cent if performed by an experienced surgeon and can be considerably lower in clinics specializing in this condition.We suggest that the pathological classification of these tumours used in this paper may form the basis for further investigations into the diagnostic and prognostic problems which these tumours present.This classification of ampullary tumours is a factor to be considered in assessing the indications for pancreaticoduodene