Background: Trastuzumab improves breast cancer survival but is associated with an increased risk of heart failure. Identifying risk factors associated with trastuzumab induced cardiotoxicity (TIC) would allow for more targeted and intensive screening for at-risk patients. Hypertension is one of the most consistent predictors of TIC. Racial/ethnic minorities are at higher risk of cardiovascular disease but are under-represented in studies of TIC. The objective of this study was to evaluate the relationship between race/ethnicity and risk of TIC among a diverse cohort of patients with HER2-positive early-stage breast cancer. Methods: We conducted a retrospective cohort study of patients treated at Columbia University between 2007 and 2016 for stage I-III breast cancer with adjuvant or neoadjuvant trastuzumab who had at least two echocardiograms. Mild TIC was defined as a ≥10% decline in left ventricular ejection fraction (LVEF); moderate TIC ≥15% decline; severe TIC ≥20% or decline in LVEF to < 50%. Diagnosis of hypertension, average systolic and diastolic blood pressure, and number of hypertension medications was assessed 1- year pre-treatment, during treatment, and 1-year post-treatment. We generated descriptive statistics and used multivariable logistic regression to evaluate demographic and clinical factors associated with TIC. Results: Of 279 patients evaluated, 36.6% were non-Hispanic white, 18.3% non-Hispanic black, 34.8% Hispanic, and 10.4% Asian. The average baseline LVEF was 60% and did not significantly differ between racial/ethnic groups. Mild TIC developed in 33.3% of patients, moderate TIC 18.6%, severe TIC 15.8%, and 14.7% with LVEF decline to < 50%. Patients with hypertension were at increased odds of developing TIC (OR = 2.41, 95% CI = 1.15-3.93; p = 0.02). Prevalence of hypertension was 53% among non-Hispanic white women, 69% non-Hispanic black, 53% Hispanic, and 39% Asian. Incidence of TIC did not differ significantly between racial/ethnic groups. Forty percent of patients with hypertension were not on any medications before initiating trastuzumab. Conclusions: There was no difference in TIC based upon race/ethnicity despite higher rates of hypertension among racial/ethnic minorities compared to non-Hispanic whites. However, a high portion of patients with hypertension were not on any medications before treatment. Increased screening and treatment of hypertension among patients receiving HER2-positive targeted therapy for early-stage breast cancer may be warranted.