The discovery of a tumour mass of the appendix, in an acute or chronic context, raises the problem of its benign or malignant, inflammatory or infectious nature. We report five cases of patients operated by the same surgical team between June 1991 and September 1996, who presented macroscopically and histologically with unusual appendicular pseudotumours: appendicular diverticulosis (n = 1), Crohn's disease localized to the appendix (n = 2), yersiniosis (n = 1), actinomycosis (n = 1). The preoperative diagnosis was acute appendicitis (n = 2) or tumour (n = 3). The postoperative course was uneventful in every case, and specific medical treatment was prescribed in two cases (yersiniosis and actinomycosis). These differential diagnoses must be considered in all appendicular diseases, but they are extremely difficult to confirm preoperatively.