Objectives.Synchronous primary cancers of the endometrium and ovary a re found in 10%of women with ovarian cancer and 5%of women with endometrial cancer. The purpose of this study was to characterize patients diagnosed with synchronous p rimary cancers of the endometrium and ovary with an emphasis on risk factors. Me thods. Between 1989 and 2002, 84 patients with synchronous primary cancers of th e endometrium and ovary were identified. Patientswith uterine papillary serous c arcinoma were excluded. Clinical and pathologic information was obtained from me dical records. Parametric methods were used to compare clinical and pathologic f eatures. Kaplan-Meier survival analyses were performed and compared using the l og rank test. Results. Median age at diagnosis was 50 years. Median body mass in dex (BMI) was 28 kg/m2. Fifty-one percent (43/84) of the women were premenopaus al and 33%(28/84)-were nulliparous. The most common presenting symptom was abn ormal vaginal bleeding; in those women with abnormal vaginal bleeding, 69%had s tage I ovarian cancer. Ovarian cancerwas an incidental finding in 48%of these p atients. Sixtyeight percent of patients (57/84) had endometrioid histology of bo th their endometrial and ovarian cancers. Patients with early stage ovarian canc er tended to have a more favorable prognosis than those with advanced stage dise ase (median survival not reached in stage I and II versus 66 months in stage III and IV, P = 0.06). Patients with concordant endometrioid histology had a favorable progno sis (median survival 119 versus 48 months in all other groups, P = 0.02). Conclu sions. In this large series of patients, women with synchronous primary cancers of the endometrium and ovary were young, obese, nulliparous, and premenopausal. Patients with concordant endometrioid tumors of the endometrium and ovary had a favorable prognosis, with median survival approaching 10 years. Objectives. Synchronous primary cancers of the endometrium and ovary a re found in 10% of women with ovarian cancer and 5% of women with endometrial cancer. The purpose of this study was to characterize patients diagnosed with synchronous p rimary cancers of the endometrium and ovary with an emphasis on risk factors. Between 1989 and 2002, 84 patients with synchronous primary cancers of th e endometrium and ovary were identified. Patients with uterine papillary serous c arcinoma were excluded. Clinical and pathologic information was obtained from me dical records. Median age at diagnosis was 50 years. Median body mass in dex (BMI) was 28 kg / m2. Fifty-one percent (43/84) of the women were premenopaus al and 33% (28/84) -were nulliparous. The most common presenting symptom was abn ormal vaginal bleeding; in those wome Sixtyeight percent of patients (57/84) had endometrioid histology of bo th their endometrial and ovarian cancers. Patients with nausea and vomiting with early stage ovarian canc er tended to have a more favorable prognosis than those with advanced stage dise ase (median survival not reached in stage I and II versus 66 months in stage III and IV, P = 0.06). Patients with concordant endometrioid histology had a favorable prognosis sis (median survival 119 versus 48 months in all other groups, P = 0.02). Conclu sions. In this large series of patients, women with synchronous primary cancers of the endometrium and ovary were young, obese, nulliparous, and premenopausal Patients with concordant endometrioid tumors of the endometrium and ovary had a favorable prognosis, with median survival approaching 10 years.