© 2016 John Wiley & Sons Ltd. Aims: To compare clinicopathological and immunohistochemical features of polypoid endometriosis (PE) and non-polypoid endometriosis (NPE). Methods and results: Fifteen cases of PE and 20 cases of NPE were assessed. All cases were stained immunohistochemically for CD10 and p16 and the proportion of p16-positive stromal and epithelial cells was estimated. On review, 10 PE cases resembled NPE histologically but occurred at mucosal or serosal surfaces, or within cyst cavities, that permitted polyp formation. These cases had a similar age distribution and immunohistochemical profile to NPE. The remaining five PE cases showed histological similarity to eutopic endometrial polyps; these occurred in older patients, and showed significantly greater stromal and epithelial p16 immunoreactivity. Conclusions: There are two main subgroups of PE. The majority of cases in this series showed similar histological features to NPE, but involved anatomical sites that facilitated exophytic or polypoid growth. The remaining PE cases resembled eutopic endometrial polyps histologically and immunophenotypically and they occurred in older patients. These findings suggest that such lesions are 'true' polyps sharing a pathogenetic relationship with similar lesions arising in the endometrium.