To determine optimal treatment for women with Stage IIIc endometrial carcinoma, extended-field radiotherapy (RT) plus chemotherapy (CT) was compared versus CT alone as adjuvant therapy. Twenty-nine patients with FIGO Stage IIIc endometrial cancer who underwent adjuvant treatment with 4.4 courses of CT (CAP or TC/DC) or 4.5 courses of CT (CAP or TC/DC) plus external pelvic RT (50 Gy) with paraaortic boost after surgery between 1992 and 2004 were retrospectively assessed. Fifteen patients underwent CT alone and 14 received combined treatment with CT/RT. Following treatment, the recurrence rate was 46.6% and 28.5% in the two treatment arms, respectively. There was a significant (p < 0.05) difference in the pelvic recurrence rate (33.3% and 7.1%, respectively). Combined treatment with RT/CT was associated with a better survival rate than CT alone (78% versus 62%, respectively). In Stage IIIc endometrial cancer, combined treatment with RT and CT reduces pelvic recurrence and improves progression-free survival and overall survival compared with CT alone.