Background: Long-term use of aromatase inhibitor (AI) therapy has been shown to decrease bone mineral density (BMD) and is associated with at least twice the fracture risk when compared to an age-matched healthy population. AI’s are a common treatment in hormone receptor-positive breast cancer for post-menopausal women. Similarly, tamoxifen has been shown to decrease BMD in premenopausal women. As a result, the National Comprehensive Cancer Network (NCCN) recommends BMD screening for women being treated with anti-estrogen therapy (AET), typically via Dual-energy X-ray absorptiometry (DEXA) scan. Previous studies have shown poor adherence to BMD screening with AI therapy, but no known study has evaluated compliance with tamoxifen therapy. Methods: We evaluated a retrospective cohort (December 2015 – July 2019) of all women with a breast cancer diagnosis initiating AET using data from the electronic health records of patients throughout a rural integrated health system. We assessed non-adherence to baseline and annual BMD screening using descriptive statistics along with preliminary data regarding fractures associated with AET therapy. Results: A total of 3,693 health records of women with a breast cancer diagnosis and documented prescription for AET were evaluated. In the year before AET initiation, 16% of women received BMD screening. Overall, 1,189 women treated with AET had a DEXA scan ordered at any point after drug initiation: 37% for AI’s and 12% for tamoxifen. Of those treated with AI, 84% had no DEXA ordered within 12 months of starting drug after a minimum of 9 months of continuous use; this value was 96% for tamoxifen use. Patients complied with the ordered DEXA scan within the first year 81% of the time. Repeat DEXA scans were ordered 34% of the time, and patient compliance decreased to 55%. There was no significant difference in the number of patient co-morbidities between patients who did and did not have a DEXA scan ordered. After starting an AI, 131 fractures were documented; 44% occurred within the first year following starting drug treatment with an average of 5 months from drug start to diagnosis. Conclusions: A significant proportion of breast cancer patients treated with AET did not receive guideline-recommended BMD screening. These findings should raise awareness of the importance of BMD screening by responsible providers, including oncologists, primary care physicians, care managers and insurance companies in order to decrease avoidable morbidity.