BACKGROUND/OBJECTIVES: This study aimed to evaluate the association between intravascular platelet aggregation in tumors and ovarian carcinoma prognosis and investigate underlying mechanisms. METHODS: A retrospective analysis was conducted on 144 patients with ovarian carcinoma. Immunohistochemical staining for CD42b, hypoxia-inducible factor-1α (HIF-1α), platelet-derived growth factor (PDGF), and vascular endothelial growth factor (VEGF) was performed using tissue microarrays to assess intravascular platelet aggregation. Staining grades ranged from 1 to 3 for CD42b (platelet aggregation or microthrombus) and 0 to 3 for HIF-1α, PDGF, and VEGF. RESULTS: Among the patients, 25 (17.4%) had grade 1 (no platelet aggregation), 85 (59.0%) had grade 2 (platelet aggregation), and 34 (23.6%) had grade 3 (microthrombus). The grade of intravascular platelet aggregation in ovarian carcinoma was statistically significantly associated with a poor prognosis ( CONCLUSIONS: Intravascular platelet aggregation in tumors is associated with advanced stages and poor prognosis in ovarian carcinoma. The results of our study suggest a potential association with hypoxia induced by intravascular platelet aggregation in ovarian carcinoma.