This study aimed to explore the effects of a decision support intervention (DSI) and shared decision making (SDM) on knowledge, perceptions about treatment, and treatment choice among men diagnosed with localized low-risk prostate cancer (PCa). At a multidisciplinary clinic visit, 30 consenting men with localized low-risk PCa completed a baseline survey, had a nurse-mediated online DS session to clarify preference for active surveillance (AS) or active treatment (AT), and met with clinicians for SDM. Participants also completed a follow-up survey at 30 days. We assessed change in treatment knowledge, decisional conflict, and perceptions and identified predictors of AS. At follow-up, participants exhibited increased knowledge (p < 0.001), decreased decisional conflict (p < 0.001), and more favorable perceptions of AS (p = 0.001). Furthermore, 25 of the 30 participants (83 %) initiated AS. Increased family and clinician support predicted this choice (p < 0.001). DSI/SDM prepared patients to make an informed decision. Perceived support of the decision facilitated patient choice of AS.