Summary Background Hysterectomy and bilateral salpingo-oophorectomy (BSO) is the standard surgery for stage I endometrial cancer. Systematic pelvic lymphadenectomy has been used to establish whether there is extra-uterine disease and as a therapeutic procedure; however, randomised trials need to be done to assess therapeutic efficacy. The ASTEC surgical trial investigated whether pelvic lymphadenectomy could improve survival of women with endometrial cancer. Methods From 85 centres in four countries, 1408 women with histologically proven endometrial carcinoma thought preoperatively to be confined to the corpus were randomly allocated by a minimisation method to standard surgery (hysterectomy and BSO, peritoneal washings, and palpation of para-aortic nodes; n=704) or standard surgery plus lymphadenectomy (n=704). The primary outcome measure was overall survival. To control for postsurgical treatment, women with early-stage disease at intermediate or high risk of recurrence were randomised (independent of lymph-node status) into the ASTEC radiotherapy trial. Analysis was by intention to treat. This study is registered, number ISRCTN 16571884. Findings After a median follow-up of 37 months (IQR 24–58), 191 women (88 standard surgery group, 103 lymphadenectomy group) had died, with a hazard ratio (HR) of 1·16 (95% CI 0·87–1·54; p=0·31) in favour of standard surgery and an absolute difference in 5-year overall survival of 1% (95% CI −4 to 6). 251 women died or had recurrent disease (107 standard surgery group, 144 lymphadenectomy group), with an HR of 1·35 (1·06–1·73; p=0·017) in favour of standard surgery and an absolute difference in 5-year recurrence-free survival of 6% (1–12). With adjustment for baseline characteristics and pathology details, the HR for overall survival was 1·04 (0·74–1·45; p=0·83) and for recurrence-free survival was 1·25 (0·93–1·66; p=0·14). Interpretation Our results show no evidence of benefit in terms of overall or recurrence-free survival for pelvic lymphadenectomy in women with early endometrial cancer. Pelvic lymphadenectomy cannot be recommended as routine procedure for therapeutic purposes outside of clinical trials. Funding Medical Research Council and National Cancer Research Network.