Objectives <p>To utilize online forums as a source of unprompted patient experiences in understanding the impacts of radiotherapy on patients with prostate cancer.</p> Materials and methods <p>Three online forums: patient.info, Cancer Survivor Network (CSN), and CancerResearchUK were identified by a structured keyword search on Google and searched for relevant posts<b>.</b> Qualitative thematic analysis using grounded-theory principles was performed on publicly available online forum posts using Dedoose (Los Angeles, CA).</p> Results <p>One hundred fifty-seven posts by 91 unique users were analyzed. The most frequently mentioned pelvic and abdominal adverse effects were “increased urine frequency” (<i>n</i> = 31) and “radiation-induced GI tract inflammation” (<i>n</i> = 28) respectively. The majority of posts showed that abdominal and pelvic adverse effects occurred after radiation treatment (<i>n</i> = 154) rather than during radiation treatment (<i>n</i> = 26). Most posts showed that patient’s symptoms were ongoing (<i>n</i> = 68) as opposed to resolving with (<i>n</i> = 35) or without (<i>n</i> = 25) treatment.</p> Conclusions <p>Online forums were frequently utilized by post-radiation prostate cancer survivors to discuss their experiences and seek peer support. This study provides physicians a deeper understanding about morbidity of post-radiation prostate cancer patients through their own narrative and highlights principal issues resonating among this patient population.</p> Implications for Cancer Survivors <p>For cancer survivors, these findings may facilitate more informed discussions with healthcare providers,&#xa0;improve awareness of potential treatment-related challenges, and underscore the value of peer support communities&#xa0;in survivorship care.</p>