Among 197 pancreatic and periampullar tumours operated between 1970 and 1979, an associated cystic of pseudocystic lesion was found on 15 occasions (a rate of 16%). In 10 cases it was a question of pseudocysts located at the bodytail, while the tumour occupied a distinct site (periampullar tumour or carcinoma of the head); in 5 cases the cavitary lesion coincided with the tumour (2 endocrine tumours of the head, 2 cystoadenocarcinomas and one adenocarcinoma of the body-tail). In 6 cases (of which 5 operated) the error in diagnosis led to misappreciation of the tumour: only 3 of these cases could be treated with radical surgery. In the other 9, correct diagnosis was possible from the start and in 6 radical surgery was performed. Stress is placed on the need for prompt and early diagnosis, in order to allow adequate treatment of the tumour in line with the canons of radical action.