Thrombocytosis(a platelet count>400,000/mm3) is found to be frequently in association with malignant disease and recently has been suggested to be a poor prognostic indicator in patients with certain cancers. The objective of this retrospective study was to determine the relevance of a preoperative platelet count in ovarian cancer with a possible prognostic significance of thrombocytosis in this disease. Between June 1989 and December 1995, eighty-five patients with epithelial ovarian cancer were evaluated, who were managed at Asan Medical Center by cytoreductive surgery and chemotherapy, and had at least 6 months' follow-up. Prevalence of thrombocytosis was 22.4% and significantly correlated with FIGO stage(p=0.003), histologic subtype(p=0.002), tumor grade(p=0.040), performance status of patient(p=0.006) and preoperative serum CA 125 level(p=0.002). And the linear regression analysis revealed a significant correlation(p<0.001) between platelet count and preoperative serum CA 125 level, which suggested that platelet count was positively associated with tumor volume. No difference in survival between patients with or without thrombocytosis was found(p=0.68), whereas residual tumor size and serum CA 125 level after 2nd chemotherapy were found to be independent prognostic factors. In conclusion, thrombocytosis is not a useful prognostic factor in epithelial ovarian cancer, but significantly associated with tumor volume.