BACKGROUND: This is an updated version of the original Cochrane review published in Issue 2, 2007. The role of radiotherapy (both pelvic external beam radiotherapy (EBRT) and vaginal intracavity brachytherapy (VBT)) in stage I endometrial cancer following hysterectomy remains controversial. OBJECTIVES: To assess the efficacy of adjuvant radiotherapy following surgery for stage I endometrial cancer. SEARCH METHODS: We searched The Cochrane Central Register of Controlled Trials (CENTRAL), MEDLINE, EMBASE and the Specialised Register to end-2005 for the original review, and extended the search to January 2012 for the update. SELECTION CRITERIA: We included randomised controlled trials (RCTs) that compared post-operative adjuvant radiotherapy (either EBRT or VBT, or both) versus no radiotherapy or VBT in women with stage I endometrial cancer. DATA COLLECTION AND ANALYSIS: Two review authors independently assessed trials and extracted data to a specifically designed data collection form. The primary outcome was overall survival. Secondary outcomes were endometrial cancer-related deaths, locoregional recurrence and distant recurrence. Meta-analyses were performed using Cochrane Review Manager Software 5.1. MAIN RESULTS: We included eight trials. Seven trials (3628 women) compared EBRT with no EBRT (or VBT), and one trial (645 women) compared VBT with no additional treatment. We considered six of the eight trials to be of a high quality. Time-to-event data were not available for all trials and all outcomes.EBRT (with or without VBT) compared with no EBRT (or VBT alone) for stage I endometrial carcinoma significantly reduced locoregional recurrence (time-to-event data: five trials, 2965 women; Hazard Ratio (HR) 0.36, 95% Confidence Interval (CI) 0.25 to 0.52; and dichotomous data: seven trials, 3628 women; Risk Ratio (RR) 0.33, 95% CI 0.23 to 0.47). This reduced risk of locoregional recurrence did not translate into improved overall survival (time-to-event data: five trials, 2,965 women; HR 0.99, 95% CI 0.82 to 1.20; and dichotomous data: seven trials, 3628 women; RR 0.98, 95% CI 0.83 to 1.15) or improved endometrial cancer-related survival (time-to-event data: five trials, 2965 women; HR 0.96, 95% CI 0.72 to 1.28; and dichotomous data: seven trials, 3628 women; RR 1.02, 95% CI 0.81 to 1.29) or improved distant recurrence rates (dichotomous data: seven trials, 3628 women; RR 1.04, 95% CI 0.80 to1.35).EBRT did not improve survival outcomes in either the intermediate-risk or high-risk subgroups, although high-risk data were limited, and a benefit of EBRT for high-risk women could not be excluded. In the subgroup of low-risk patients (IA/B and grade 1/2), EBRT increased the risk of endometrial carcinoma-related deaths (including treatment-related deaths) (two trials, 517 women; RR 2.64, 95% CI 1.05 to 6.66) but there was a lack of data on overall survival. We considered the evidence for the low-risk subgroup to be of a low quality.EBRT was associated with significantly increased severe acute toxicity (two trials, 1328 patients, RR 4.68, 95% CI 1.35 to 16.16), increased severe late toxicity (six trials, 3501 women; RR 2.58, 95% CI 1.61 to 4.11) and significant reductions in quality of life scores and rectal and bladder function more than 10 years after randomisation (one trial, 351 women) compared with no EBRT.One trial of VBT versus no additional treatment in women with low-risk lesions reported a non-significant reduction in locoregional recurrence in the VBT group compared with the no additional treatment group (RR 0.39, (95% CI 0.14 to 1.09). There were no significant differences in survival outcomes in this trial. AUTHORS' CONCLUSIONS: EBRT reduces the risk of locoregional recurrence but has no significant impact on cancer-related deaths or overall survival. It is associated with significant morbidity and a reduction in quality of life, and bladder and rectal function. EBRT may have an adverse effect on endometrial cancer survival when used to treat uncomplicated low-risk (IA/B grade 1/2) endometrial cancer. There is no demonstrable survival advantage from adjuvant EBRT for high-risk stage I endometrial cancer, however, the meta-analyses of this subgroup were underpowered and also included high-intermediate risk women. Further research is likely to have an important impact on our confidence in the estimates of effects and may change the estimates. Therefore, whilst there appears to be no survival benefit in the routine use of EBRT in women with stage I endometrial cancer, we cannot exclude a benefit in high-risk women. VBT is potentially useful in intermediate-risk and high-risk subgroups but evidence from further RCTs is needed. In addition, the definitions of risk should be standardised.