Introduction Androgen deprivation therapy (ADT) remains a cornerstone in treatment for patients with advanced prostate cancer. ADT is associated with several adverse effects including osteoporosis, metabolic syndrome, and cardiovascular events, leading to guidelines recommending routine testing to monitor for these toxicities. There is a lack of data assessing adherence to these recommendations. Methods We conducted an observational, retrospective cohort study utilizing administrative data sources in Ontario, Canada between 2008-2021. We identified all men receiving ADT for prostate cancer. The primary outcomes were use of lipids, dysglycemia (glucose), bone health serum and bone density testing between 6 weeks preceding and 1 year following initiation of ADT. Secondary outcomes included predictors of adherence to testing. Results We examined 29,097 patients of whom 52.8% were prescribed ADT by Urologists, 37.9% by Radiation Oncologists, 2.8% by Medical Oncologists, and 2.4% by other physicians. Adherence to guidelines was generally low: only 21.3% of patients received a bone density scan, 41.2% underwent bone-health-related serum tests, 51.3% had a lipid profile completed, and 65.9% underwent dysglycemia testing within 1 year of diagnosis. Overall, only 11.9% of patients received all the recommended investigations. Adherence to testing did not appear to improve over time (2008-2021) or with the publication of guidelines. Patient (age) and physician (specialty) factors showed important associations with adherence to testing. ADT prescription by a Medical Oncologist was associated with a lower likelihood of undergoing screening tests for plasma glucose (RR 0.78, 95% CI 0.64-0.96, p=0.02), lipids (RR 0.65, 95% CI 0.58-0.80, p=<0.01) and bone density (RR 0.62, 95% CI 0.43-0.89, p=0.009) within a year when compared to prescription by Urologists. Increasing patient age was associated with lower adherence to screening guidelines for lipids (RR 0.26, 95% CI 0.12-0.62, p=0.002) and bone health (RR 0.37, 95% CI 0.17-0.83, p=0.016). Conclusions Most patients receiving ADT for prostate cancer do not receive recommended testing to monitor for treatment-related toxicity. Further study is required to identify and address barriers to therapeutic monitoring of men on ADT and reduce treatment-associated adverse events.