Patients with polycythemia vera (PV) and essential thrombocythemia (ET) have increased thrombotic risk. This retrospective, real-world analysis of Medicare patients (age ≥ 65 years) newly diagnosed with high-risk PV or intermediate-/high-risk ET compared mortality risk among those with versus without thrombotic events during the study period. Patients diagnosed with PV or ET with ≥ 1 inpatient or ≥ 2 outpatient claims (January 1, 2010–December 31, 2017; index was date of first qualifying claim) were included. The study included 50,405 Medicare beneficiaries with PV and 124,569 with ET. During follow-up (median range: PV, 34.5 0–97.3 months; ET, 25.5 0–97.4 months), 14,334 patients (28.4%) with PV and 30,478 (24.5%) with ET experienced thrombotic events (most commonly ischemic stroke PV, 46.0%; ET, 42.5%. Mortality risk was increased for patients with versus without post-index thrombosis for both PV (adjusted hazard ratio aHR; 95% CI, 18.6 16.1–21.6; P < 0.001) and ET (aHR 95% CI, 25.2 23.1–27.5; P < 0.001). Median survival was shorter for patients who experienced a thrombotic event ≤ 1 year post-index versus those who did not (PV, 5.1 years vs not reached; ET, 3.7 vs 6.7 years; both P < 0.001). These findings highlight the importance of thrombosis risk mitigation in PV and ET management. Display omitted •Patients with PV and ET have increased risk for thrombotic events (TEs).•We compared mortality risk among patients with PV or ET with vs without TEs.•During follow-up (PV, 35 mo; ET, 26 mo), 28% (PV) and 24% (ET) of patients had a TE.•Mortality risk was higher and survival was shorter among those with vs without TEs.