Objectives Cardiovascular disease (CVD) is of increasing concern among breast cancer survivors. However, evidence on ethnic differences in CVD among women with breast cancer is sparse. We assessed ethnic differences in cardiovascular morbidity and mortality among patients with breast cancer in the Netherlands. Methods A nationwide register-based cohort study comprising all women with a first admission for breast cancer (n=127 714) between 1996 and 2010 in the Netherlands was conducted. Differences in CVD admission, CVD mortality and overall CVD event, which comprised a CVD admission and/or CVD mortality, between the largest ethnic minority groups (Surinamese, Moroccan, Turkish, Antillean and Indonesian) and the Dutch general population (henceforth, Dutch) were investigated using Cox proportional hazard models. Results The incidence of cardiovascular outcomes varied by the ethnic group. The incidence of an overall cardiovascular event was significantly higher for women with breast cancer from Suriname (HR 1.46; 95% CI 1.29 to 1.64) and Turkey (HR 1.25; 95% CI 1.03 to 1.51), compared with Dutch women with breast cancer. In contrast, Indonesian women with breast cancer had a significantly lower risk (HR 0.88; 95% CI 0.81 to 0.96) of a cardiovascular event compared with Dutch women with breast cancer. The risk of a cardiovascular event did not differ between Moroccan and Dutch women with breast cancer, whereas for Antillean women the risk was not significantly higher. Conclusions Our findings suggest that Surinamese and Turkish women with breast cancer are disadvantaged in terms of cardiovascular outcomes compared with Dutch women with breast cancer. More work is needed to unravel the potential factors contributing to these differences.