Fairman, CM, LaFountain, RL, Lucas, AR, and Focht, BC. Monitoring resistance exercise intensity using ratings of perceived exertion (RPE) in previously untrained patients with prostate cancer undergoing androgen deprivation therapy. J Strength Cond Res 32(5): 1360–1365, 2018—Exercise has been shown to be safe and effective for patients with prostate cancer (PrCa). The monitoring of resistance exercise (RE) intensity is an emerging area of interest in RE prescription. Rating of perceived exertion (RPE) is one of the most commonly used methods but has not yet been validated in this population. Thus, the purpose of this study was to examine the relationship between RPE and RE intensity in PrCa. Data for this study were abstracted from baseline upper- and lower-body strength assessments from 2 previous trials (Individual Diet and Exercise Adherence Pilot Trial; Livestrong, Austin, TX, USA) in our laboratory investigating functional outcomes in patients with PrCa undergoing androgen deprivation therapy (ADT). A total of 75 participants from both trials were included in this study. Ratings of perceived exertion corresponding to 50, 70, and 90% 1 repetition maximum (1RM) were extracted from the results of participants' upper- and lower-body 1RM strength tests. The changes in RPE across increasing intensities were assessed using separate univariate analysis of variance (ANOVA). For each ANOVA, RPE was used as the dependent variable and intensity (50, 70, and 90%) used as the fixed factor. A univariate ANOVA revealed a significant difference (p ≤ 0.05) among the RPE values for each intensity for both upper- and lower-body lifts. The results of our analyses suggest that RPE values rise linearly in response to increases in exercise intensity. Our study supports the concept that RPE may be a practical training tool to accurately estimate RE intensity in PrCa survivors undergoing ADT. Practitioners may consider using RPE to monitor and adjust RE intensity in this population.