Objective: To determine the outcomes in patients with Stage I uterine clear cell carcinoma (UCCC) treated with and without adjuvant therapy, and to compare the outcomes in these patients to that of matched controls, patients with Stage I, grade 3, endometrioid adenocarcinoma of the endometrium (EC). Methods: Patients with FIGO Stage I UCCC who underwent comprehensive surgical staging between January 1996 and January 2007 were identified. Cases (UCCC) were matched by age, stage, adjuvant therapy, and year of diagnosis to controls consisting of patients with grade 3 EC. Recurrence and survival were analyzed using the Kaplan- Meier method. Results: 25 patients with Stage I UCCC were identified of whom 13 (52%) received no adjuvant therapy and 12 (48%) received adjuvant radiation therapy (XRT). The 5-year disease-free survival and overall survival rates for the observation and the XRT groups were 78% and 75%, (p = 0.7) and 85% and 82% (p = 0.1), respectively. When compared to controls, the 5-year disease-free survival rates and overall survival rates of patients with Stage I UCCC were not significantly different, 77% vs 75% (p = 0.8) and 84% vs 88% (p = 0.5), respectively. Conclusions: In patients with Stage I UCCC tumors there was no clear benefit to adjuvant radiation given the absence of improvement in recurrence risk or any survival benefit. These data question the benefit of radiation therapy in UCCC patients with disease confined to the uterus.