Background: Prostate radiotherapy is associated with worse oncologic outcomes in patients with bladder cancer. This is thought to be secondary to microvascular damage resulting in propagation of inflammation. There is sparse data on the effect of prior radiotherapy on the efficacy of intravesical Bacillus Calmette-Guerin (BCG) in patients with non-muscle invasive bladder cancer (NMIBC). We sought to evaluate BCG response and outcomes in NMIBC patients who have previously undergone prostate radiotherapy compared to patients with no prior history of pelvic radiotherapy. Methods: This is a retrospective cohort study that includes patients who received intravesical BCG for NMIBC at our institution from 2001 to 2019. Data were collected on patient and pathologic characteristics. Patients were stratified into three cohorts: prior radiotherapy (RT), radical prostatectomy (RP), and no prostate cancer (No PCa). Wilcoxon rank sum test and Chi-squared test were used for comparison between groups. The primary endpoints included recurrence at one-year, progression to MIBC and progression to metastatic disease. Results: In 199 total patients who underwent BCG for NMIBC, 23 had a prior history of radiotherapy treatment for prostate cancer, while 17 underwent prior radical prostatectomy. Overall, 41.2% of patients had recurrence at one year. There was no difference in recurrence at one year between the cohorts: 42.8% No PCa, 29.4% RP and 39.1% RT; p = 0.56. There was also no difference in progression to MIBC (6.9% No PCA, 0% RP, and 8.7% RT) or progression to metastatic disease (6.9% No PCA, 5.9% RP and 4.3% RT) with p = 0.50 and 0.89 respectively. Conclusions: The efficacy of intravesical BCG does not appear to be modified by prior radiation treatment for prostate cancer in patients with NMIBC.