Objectives: Adjuvant treatment for stage III endometrial cancer is not yet defined. Previous experiences support the usefulness of combined chemotherapy and radiotherapy. The aim of this retrospective study was to describe the outcome in a cohort of patients with stage III endometrial cancer treated with chemotherapy and/or radiotherapy. Methods: A multicenter retrospective analysis of patients with stage III endometrial cancer from 1998 to 2009 was conducted. The impact on relapse-free survival of clinical and pathological variables and adjuvant treatment received was analyzed by univariate and multivariate analysis. Results: Eighty-two patients were considered. Median age was 62 years (range 38–82). Seventy-eight (95%) patients received an adjuvant treatment: chemotherapy (41; 50%), radiotherapy (18; 22%), or combined chemo-radiotherapy (19; 23%). Four patients were excluded from analysis because they were not treated with any adjuvant therapy. At univariate analysis, tumor grade (G3 vs. G1–G2; p = 0.003) was associated with risk of recurrence; similarly, patients treated with radiotherapy alone (p = 0.031, hazard ratio 0.19, 95% CI 0.04–0.86) or chemotherapy alone (p = 0.053, hazard ratio 0.54, 95% CI 0.29–1.01) had a significantly higher risk for relapse, compared to those treated with the multimodality approach. Relapse-free survival at 3 years was 86.5, 65.8 and 44.1%, with the multimodality approach, chemotherapy and radiotherapy, respectively. At multivariable analysis, age and grading were independently associated with recurrence-free survival. Hazard ratio for relapse-free survival was 0.14 (95% CI 0.02–1.04) and 0.20 (95% CI 0.04–1.11) for multimodality treatment compared to chemotherapy alone and radiotherapy alone, respectively. Conclusions: Age and grading are independent prognostic factors. A combined approach with radiotherapy and chemotherapy may induce an advantage in relapse-free survival compared to radiotherapy or chemotherapy alone. Prospective clinical trials are needed to verify this clinical hypothesis.