A 10-year retrospective review of epithelial carcinoma of the ovary was performed about 95 patients which were diagnosed and treated at the Oita Medical University Hospital. The patients' ages at the first diagnosis ranged from 15 to 85 years with a mean of 51.6 years. Twenty-two of 95 patients (23.2%) were below the age of 40. Most patients analysed in this study complained of lower abdominal pain, lower abdominal mass, and/or lower abdominal fullness. Sixteen of 22 patients under the age of 40 (72.7%) and 27 of 73 patients over the age of 40 (37.0%) were diagnosed as having mucinous cystadenocarcinoma. The incidence of mucinous cystadenocarcinoma below the age of 40 was significantly higher than that over the age of 40 (p < 0.005, chi 2-test). Eleven patients below the age of 40 had FIGO stage Ia grade 1 disease and 2 of these patients were pregnant. The incidence of stage Ia disease under the age of 40 was significantly higher than that over the age of 40 (p < 0.005, chi 2-test). Both pregnant patients and 5 other patients with stage Ia disease were treated with only unilateral salpingo-oophorectomy. All patient with stage Ia disease had no evidence of recurrence within 5 years. This suggests that conservative surgery may be considered as the treatment for the FIGO stage Ia grade 1 ovarian cancer.