In recent years, ovarian cancer has been increasing in Japan. However, a mass-screening system for ovarian cancer is not yet established. For this reason, detection of early ovarian cancer is very difficult. 1. Due to the low frequency of ovarian cancer detection, a mass-screening system is not cost-effective. 2. There is no accurate method for the detection of ovarian cancer, as with cytology or colposcopy for the detection of uterine cancer. We describe some methods for the detection of ovarian cancer by mass screening, and point out some problems. Tumor marker is not always useful because of its low sensitivity for early ovarian cancer. It is most important to determine whether or not an ovarian tumor is present. We attempted to detect ovarian tumors at the time of uterine cancer mass screening by ultrasonography (transvaginal proof). Three early ovarian cancers were detected in 10,294 women.