Background: To study the incidence of non-endometrioid carcinoma of endometrium and compare the clinical characteristics and treatment outcomes with endometrioid carcinoma patients. Materials and Methods: This study included 236 patients with endometrial carcinoma at Siriraj Hospital whom were diagnosed and treated from 2003 through 2006. The clinical characteristics, pathological features, treatment and clinical outcomes were collected from the medical records. The 5-year survival was calculated according to 2009 FIGO staging. Results: Non-endometrioid carcinoma of endometrium accounted for 10.2% of all endometrial carcinomas (24/236 patients). The 5-year survival rate was significantly lower in the non-endometrioid group compared to the endometrioid group (77.3% vs 96%, p<0.001) and clinical data pointed to greater malignancy. Conclusions: Non-endometrioid carcinoma of endometrium is relative rare but is more aggressive, has more distant metastasis at diagnosis with a worse survival rate than endometrioid carcinoma. Only patients in stage IA with no residual disease on a hysterectomy specimen may not need adjuvant treatment.