BACKGROUND: Previous ischemic stroke (IS) is a risk factor for subsequent IS in the general population; it is unclear if this relationship remains true in patients with cancer. Our objective was to examine the association between previous IS and risk for future IS in individuals newly diagnosed with cancer. METHODS: We conducted a retrospective population-based matched cohort study of newly diagnosed adult cancer patients (excluding nonmelanoma skin cancers and primary central nervous system tumors) in Ontario, Canada from 2010 to 2020; those with prior IS were matched (1:4) by age, sex, year of cancer diagnosis, cancer stage, and cancer site to those without a history of stroke. Cumulative incidence function curves were created to estimate the incidence of IS. Subdistribution adjusted hazard ratios (aHRs) and 95% CIs were calculated, where death was treated as a competing event. Multivariable analysis was adjusted for imbalanced baseline characteristics. RESULTS: We examined 65 525 individuals with cancer, including 13 070 with a history of IS. The median follow-up duration was 743 days (interquartile range, 177–1729 days). The incidence of IS following cancer diagnosis was 261.3/10 000 person-years in the cohort with prior IS and 75.3/10 000 person-years in those without prior IS. Individuals with prior IS had an increased risk for IS after cancer diagnosis compared with those without a history (aHR, 2.68 [95% CI, 2.41–2.98]); they also had more prevalent cardiovascular risk factors. The highest risk for stroke compared with those without a history of IS was observed in the gynecologic cancer (aHR, 3.84 [95% CI, 2.15–6.85]) and lung cancer (aHR, 3.18 [95% CI, 2.52–4.02]) subgroups. The risk of IS was inversely correlated with lag time of previous stroke; those with IS 1 year before their cancer diagnosis had the highest risk (aHR, 3.68 [95% CI, 3.22–4.22]). CONCLUSIONS: Among individuals with newly diagnosed cancer, those with IS history were almost 3× more likely to experience a stroke after cancer diagnosis, especially if the prediagnosis stroke occurred within 1 year preceding cancer diagnosis.