Background: Cardiovascular disease (CVD) occurs frequently in men with prostate cancer (PC), but the reasons are unclear. Specifically, the role of androgen deprivation therapy (ADT) in promoting CVD remains uncertain. There is a lack of evidence to inform preventive strategies against CVD in this high risk group. It is unknown if the evidence to support CVD preventive strategies in the general population can be validly extrapolated to men with PC. Methods: RADICAL-PC combines two prospective studies, one of which is embedded in the other. The Role of Androgen Deprivation Therapy in Cardiovascular Disease – A Longitudinal Prostate Cancer Study (RADICAL PC1) is a prospective cohort study of men within one year of their first diagnosis of PC, or who are within one month of commencing ADT for the first time. Its goal is to identify factors associated with the development of CVD among men with PC, with a particular focus on ADT. The Randomized Intervention for Cardiovascular and Lifestyle Risk Factors in Prostate Cancer Patients (RADICAL PC2) is a randomized, controlled trial embedded in RADICAL PC1. RADICAL PC2 will test a systematic approach to modifying CV and lifestyle risk factors. The intervention group will receive: 1) Standardized advice on healthy diet and exercise; 2) Low-dose antiplatelet agent; 3) Low- to moderate-dose statin; and 4) ACE-I for baseline systolic blood pressure ≥ 130mmHg. Results: The study has been recently funded by Movember clinical trial program of Prostate Cancer Canada, and is launched across Canada. The primary outcome is the occurrence of the composite of cardiovascular death, myocardial infarction, stroke, heart failure, or arterial revascularization. For RADICAL-PC1, 6000 participants will have 90% power to detect a hazard ratio 0.86 for a given exposure. For RADICAL-PC2, 4116 participants randomized, with 434 primary outcome events will have 85% power to detect a hazard ratio of 0.75 in the intervention group. Conclusions: RADICAL PC will be one of the largest prospective studies of CVD – the main competing risk – in men with PC. It will clarify the determinants of CVD in these men, the role of ADT in CVD, and will simultaneously test an intervention to lower the CVD risk in this high-risk population.