Objective. Studies in several solid tumors have shown that the presence of occult metastasis in the bone marrow or peripheral blood is highly predictive of decreased disease-free and overall survival. Our objective was to determine the incidence of circulating ovarian or primary peritoneal cancer cells in the peripheral blood at the time of disease diagnosis, or recurrence, and to determine the prognostic significance of these occult metastasis. Methods. Peripheral blood was drawn preoperatively from 91 women thought to have newly diagnosed or recurrent epithelial ovarian or primary peritoneal carcinoma. All samples underwent a tumor-enriched immunocytochemical assay. Results. Sixty-four women were found to have epithelial ovarian or primary peritoneal cancer. Of the 64 women with cancer, 12 had evidence of circulating cancer cells in their peripheral blood (18.7%). Characteristics were compared between those with circulating cancer cells and those without, using Fisher's exact test or the Wilcoxon-Mann-Whitney test, as appropriate. Women with circulating cancer cells had statistically more grade 3 tumors than women without. At a mean follow-up of 18.7 months (SD 6.7 months), analysis using Kaplan-Meier estimation and the log-rank test indicated that survival curves did not differ between patients with and without circulating cancer cells. Conclusion. Ovarian and primary peritoneal cancer, which historically has been thought to spread primarily by direct cell seeding throughout the abdominal cavity, can have circulating cancer cells in the peripheral blood. The clinical utility of identifying circulating cancer cells is yet to be defined.