The relative frequency of ovarian neoplasms varies according to information in different texts. In an attempt to clarify the distribution of primary ovarian neoplasms by decades of life, a 10-year retrospective review of 861 women with a postoperative diagnosis of an ovarian neoplasm was undertaken. Benign cystic teratoma was the single most common ovarian neoplasm, accounting for 44% of all neoplasms, and was 57% more frequent than benign serous tumors. Germ cell neoplasms were the most common group of benign ovarian neoplasms; epithelial neoplasms were the most common malignant neoplasm. Stromal neoplasms and neoplasms of low malignant potential were uncommon at all ages. The risk that an ovarian neoplasm was malignant increased 12-fold from ages 20-29 to 60-69. The overall risk that an ovarian neoplasm was malignant was 13% in premenopausal women and 45% in postmenopausal women.