BACKGROUND: We compared survival outcomes and risk of venous thromboembolism (VTE) among patients with advanced and early-stage ovarian clear cell carcinoma (OCCC) and serous ovarian carcinoma (SOC), as well as potential links with interleukin-6 (IL-6) levels. METHODS: A multicenter case-control study was conducted in 370 patients with OCCC and 938 with SOC. In a subset of 200 cases, pretreatment plasma IL-6 levels were examined. FINDINGS: Patients with advanced OCCC had the highest 2-year cumulative VTE rates (advanced OCCC 43.1%, advanced SOC 16.2%, early-stage OCCC 11.9% and early-stage SOC 6.4%, P<0.0001) and the highest median levels of IL-6 (advanced OCCC 17.8 pg/mL, advanced SOC 9.0 pg/mL, early-stage OCCC 4.2 pg/mL and early-stage SOC 5.0 pg/mL, P=0.006). Advanced OCCC (hazard ratio [HR] 3.38, P<0.0001), thrombocytosis (HR 1.42, P=0.032) and elevated IL-6 (HR 8.90, P=0.046) were independent predictors of VTE. In multivariate analysis, patients with advanced OCCC had significantly poorer 5-year progression-free and overall survival rates than those with advanced SOC (P<0.01), and thrombocytosis was an independent predictor of decreased survival outcomes (P<0.01). Elevated IL-6 levels led to poorer 2-year progression-free survival rates in patients with OCCC (50% versus 87.5%, HR 4.89, P=0.016) than in those with SOC (24.9% versus 40.8%, HR 1.40, P=0.07). INTERPRETATION: Advanced OCCC is associated with an increased incidence of VTE and decreased survival outcomes, which has major implications for clinical management of OCCC.