Background: HER2-positive breast cancer historically carried a poor prognosis, though the development of HER2-targeted agents has greatly improved clinical outcomes. The APHINITY trial demonstrated a small but statistically significant improvement in invasive disease-free survival in high-risk patients with HER2-positive breast cancer with the addition of one year of pertuzumab (P) to trastuzumab (T) compared to T alone, particularly in node-positive and hormone receptor negative disease. The purpose of this study was to identify variables influencing administration of P in our health system. Methods: We performed a retrospective chart review of patients diagnosed with breast cancer without metastatic disease who received T between July 2016 and April 2019 at University of Colorado Health hospitals. We collected information on the receipt of P, intended duration of P, and other clinical and demographic factors. Results: A total of 350 patients were identified with stage I-III HER2-positive breast cancer receiving adjuvant T; 93 patients (26.6%) were prescribed P in the adjuvant setting with intent to complete 1 year. 78 patients (84.8%) given adjuvant P were T2 or higher. 25.3% of all ≥T2, node-negative and 41.6% of all node-positive patients received adjuvant P. Patients receiving P were more likely to be younger (average age 48.1 versus 56.5, P<0.0001) and premenopausal (52.7%). 34.7% of patients at the academic hospital received adjuvant P versus 22% at community clinics (P=0.01). Hormone receptor status and prior pathologic complete response to neoadjuvant chemotherapy (if given) did not correlate with P administration. Conclusions: In our study, the use of adjuvant P was common in high-risk patients including premenopausal women and those with node-positive disease, as well as those treated at the academic site. This practice pattern is supported by the APHINITY trial results and NCCN guidelines. However, the majority of node-positive patients, and many hormone receptor-negative patients did not receive adjuvant P. With continued follow-up, this dataset will allow us to evaluate the use of other adjuvant HER2-targeted therapy, including trastuzumab emtansine and neratinib.