This study investigates the rate of endometrial carcinoma found at hysterectomy in women with a biopsy diagnosis of atypical endometrial hyperplasia, in the John Radcliffe Hospital, Oxford. The Gynecologic Oncology Group (GOG) recently reported a rate of 42.6% in a large prospective study in the USA (Trimble et al. 2006). This retrospective study has identified a similar rate of 45.9% at the John Radcliffe. There is much interest in conservative therapies for atypical endometrial hyperplasia, but with such a high incidence of endometrial carcinoma in cases of atypical endometrial hyperplasia diagnosed by endometrial biopsy, it would seem prudent to exercise caution when considering any conservative therapy.