Aims: A review of the literature indicated that only one case of serrated adenoma of the appendix has been recorded. The aim was to explore the possible occurrence of serrated adenomas of the appendix at the department of pathology, Karolinska Institute and University Hospital, Stockholm, Sweden. Methods: Between January 1993 and December 2003, 38 non-carcinoid, non-neoplastic, or neoplastic polyps or tumours of the appendix were surgically removed at this hospital. All filed histological sections (haematoxylin and eosin stained) were reviewed. Results: Of the 38 lesions, four were hyperplastic polyps, 10 serrated adenomas, six villous adenomas, and the remaining eight mucinous adenocarcinomas without a remnant adenoma. Serrated adenomas accounted for six of the 11 adenomas without invasion, and four of the 15 adenomas with invasive carcinoma. At the time of surgical resection, four of the 10 serrated adenomas had evolved into invasive carcinomas, in addition to 11 of the 16 villous adenomas. Conclusions: Serrated and villous adenomas of the appendix appear to be highly aggressive lesions, more aggressive than similar adenomas in the colon and rectum. Of the seven cases with a hyperplastic polyp, one concurred with a serrated adenoma, two with a serrated adenoma having an invasive carcinoma, and one with invasive carcinoma without a remnant adenomatous structure. At present, there is an increased awareness that some hyperplastic polyps of the colon and rectum may evolve into serrated adenomas. Whether this pathway is also valid for the appendix vermiformis should be investigated in a larger number of cases.