Background: Doxorubicin-cyclophosphamide (AC), docetaxel-cyclophosphamide (TC), and AC followed by or preceded by docetaxel or paclitaxel (ACT) are common adjuvant chemotherapies for early stage breast cancer. We aimed to assess how adjuvant AC, TC, and ACT differ with regard to early and later acute care use, both of which may be surrogates for severe toxicity. Methods: We utilized administrative claims data from a large U.S. commercial insurance database (OptumLabs) to retrospectively identify privately insured and Medicare Advantage-insured women with early stage breast cancer who received adjuvant AC, TC, or ACT during 2005-2013 (using validated claims-based algorithms). We analyzed billing data 0-6 and 6-12 months after the first dose of chemotherapy to examine rates of hospitalizations and emergency room (ER) visits. We used Poisson regression models to calculate rates of acute care use adjusted for age, race, and Charlson comorbidity score at diagnosis. Results: We identified 4,501 patients; 1,785 received TC, 644 AC, and 2,072 ACT. Average age at diagnosis was 53 years. Overall, 17% were hospitalized and 21% were seen in the ER without a subsequent hospitalization within 12 months of the start of the chemotherapy. In total, there were 983 hospitalizations and 1281 ER visits in this population. Please see the Table for differences between regimens in acute care use. Conclusions: Patients who receive adjuvant AC, TC, and ACT for breast cancer have different needs for acute care. This may reflect treatment assignment bias or unequal risks of severe toxicity. Further characterization of these events may help inform treatment decisions.