Purpose To examine whether stroke risk is elevated in American breast cancer patients treated with modern techniques, as well as whether supraclavicular radiation therapy (RT) is associated with increased risk. Methods Observed rates of stroke in 820 eligible early-stage breast cancer patients treated at the University of Michigan Hospital (Ann Arbor, MI) were compared with expected rates. Relationships between potential risk factors and actuarial rate of first stroke were analyzed. Results Median follow-up was 6.8 years. Twenty patients had at least one cerebrovascular accident (CVA) in follow-up; 35 patients had at least one CVA or transient ischemic attack (CVA/TIA). The standardized incidence ratios were 1.74 (0.94 to 2.37) for CVA and 1.68 (1.003 to 2.06) for CVA/TIA. The absolute excess risk per 1,000 patients per year was 1.67 for CVA and 2.76 for CVA/TIA. On bivariate analysis, factors significantly associated with actuarial rate of first CVA included hypertension (P = .002), age (P < .0001), coronary artery disease (P = .001), atrial fibrillation (P = .009), and supraclavicular RT (P = .021). Factors associated with CVA/TIA were hypertension (P < .001), coronary artery disease (P = .002), and age (P < .0001). Tamoxifen use alone was not significant (P = .19), but tamoxifen combined with baseline hypertension led to increased risk of CVA/TIA (log-rank P < .0001). On multivariate analysis, only age (P < .001) and hypertension (P = .003) remained significant predictors of CVA/TIA. Age was the only significant predictor of CVA alone (P < .001). Conclusion American breast cancer survivors may have an elevated risk of stroke compared with the general population, but the absolute excess risk is low. This study found no significant association between supraclavicular RT and stroke after controlling for other factors.