Background: Early Breast Cancer Trialist Collaborative Group meta-analysis suggested significant reduction in bone metastasis and breast cancer mortality among post-menopausal women diagnosed with early breast cancer when treated with an adjuvant bisphosphonate. Cancer Care Ontario and American Society of Clinical Oncology clinical practice guideline published in 2017, recommends the use of an adjuvant bisphosphonate in postmenopausal women who are candidates for adjuvant systemic therapy. Our goal was to evaluate trends and factors associated with adjuvant bisphosphonate usage since the guideline’s publication. Methods: This study is a retrospective review of postmenopausal women treated for early breast at the London Regional Cancer Program from 2017-2018. Univariate and a multivariable logistic regression models were used to investigate factors potentially associated with adjuvant bisphosphonate use including age, stage, grade, estrogen receptor, progesterone receptor, HER2 receptor status and previous use of adjuvant chemotherapy. The percentage of patients offered, receiving and declining therapy was also recorded and the time interval from surgery to start of bisphosphonate therapy (< 6 months, 6-12 months or >12 months). Results: We identified 286 postmenopausal breast cancer patients, of whom 75 (28%) received adjuvant bisphosphonate therapy. In our multivariable model, cancer stage [odds ratio (OR) stage II vs. I=2.26, 95% confidence interval (CI) 1.08-4.74) and OR Stage III vs. I=4.94, 95% CI 1.84-13.17] and previous use of adjuvant chemotherapy (OR=2.76, 95%CI 1.37-5.55) were significantly associated with adjuvant bisphosphonate use. Among 133 patients who received adjuvant systemic chemotherapy, 51% were offered adjuvant bisphosphonate and of these 81% patients accepted therapy. Among a total of 75 patients receiving adjuvant bisphosphonate therapy 19% initiated therapy within 6 months of surgery, 48% within 6-12 months of surgery, and 33% after 12 months following surgery. Conclusions: Stage and previous use of chemotherapy were significantly associated with adjuvant bisphosphonate therapy. Our study observes the potential underutilization of adjuvant bisphosphonate therapy and possible need to start treatment earlier in some patients. Further education and awareness of the clinical practice guidelines regarding adjuvant bisphosphonate therapy may be warranted and additional population-based study investigating treatment patterns and real-world effectiveness.