The authors summarize the difficulties in diagnosis some tumour-like lesions or digestive tumours. They rely upon thirty years experience in digestive pathology and upon a survey of relevant literature. They recall the difficulties arising from the inflammatory tumour-like lesions (infiltrating sclerosis or granulomas, colitis cystica profunda, inflammatory polyps). They mention the circumstances which bring about errors or incomplete diagnosis among these very tumours. Some difficulties are due to the circumstances in which these tumours appear : the digestive cancers of the child, the assocations of some family cancers (the ill-forming tumours and the dysembryoplasic cancers, and lastly the connections that exist between some inflammatory or dystrophic diseases and tumours. Other difficulties depend upon the topography or the tumorous structure. Paneth-cell carcinomas, goblet cell carcinoid are chosen as instances among epithelial tumours. In the group of non-epithelial tumours, digestive localizations of angiomatosis and of lymphomatosis may cause errors. Likewise this can be applied to some secondary digestive tumours. Regarding these difficulties, the authors stress the necessity of a close cooperation between gastro-enterologists, surgeons and pathologists. They also stress the strict observance of techniques in fixation and preparation of specimens and biopsies, and also the necessity of completing, if need be, the habitual microscopy through more elaborate explorations (histochemistry, electron microscopy...).