Background: Patients with localized prostate cancer (PCa) assimilate information from varying sources to inform their treatment decision. We assessed the impact of the primary information source used to select a modern radiation treatment on patient perceptions of their treatment experience and on treatment regret. Methods: Patients with favorable-risk PCa treated with SBRT, IMRT or HDR brachytherapy and at least one year of follow-up were surveyed. The questionnaire explored the decision-making experience, expected treatment experience vs. the reality, and treatment regret via a validated tool. Multivariate logistic regression adjusted for demographics, disease characteristics, treatment modality, time since treatment and current bowel, urinary and sexual function. Results: 322 consecutive patients were surveyed with an 86% (n = 276) response rate. 48% (n = 132) selected their radiation oncologist as the primary information source, 23% (n = 62) selected their urologist, 16% (n = 44) selected the internet, 6% (n = 17) selected other patients and 8% (n = 21) selected other. Overall, 13% (n = 36) endorsed treatment regret. 39% of patients who selected the internet as their primary information source reported their actual treatment experience to be worse than expected vs. 13% of respondents who selected their urologist, 12% who selected other patients, 2% who selected their radiation oncologist and 9% who selected other (p< 0.01). Similarly, 43% who selected the internet as their primary information source endorsed treatment regret vs. 10% who selected their urologist, 7% who selected their radiation oncologist, 6% who selected other patients and 6% who selected other (p< 0.01). On multivariate logistic regression, only patients who selected the internet as their primary information source were more likely to endorse treatment regret (OR = 46.5, p< 0.01) and were more likely to choose a treatment they thought ‘had the least side effects’ (OR = 2.1, p= 0.016). Conclusions: Patients who used the internet as their primary source of information had a worse perception of their treatment experience and had more treatment regret, highlighting the need for physicians to proactively counsel patients.