The benefit of adding sentinel node biopsy (SNB) to extended pelvic lymph node dissection (ePLND) remains controversial. The aim of our study was to evaluate biochemical recurrence (BCR) after robot-assisted radical prostatectomy and ePLND in prostate cancer patients, stratified by the application of SNB. The results were compared with the predictions of the updated Memorial Sloan Kettering Cancer Center nomogram. Methods: Between January 2006 and November 2016, 920 patients underwent robot-assisted radical prostatectomy and ePLND with or without SNB (184 and 736 patients, respectively). BCR was defined as 2 consecutive prostate-specific antigen rises of at least 0.2 ng/mL. The Kaplan-Meier method and Cox regression analyses were used to identify predictors of BCR. Results: Median follow-up was 28 mo (interquartile range, 13-56.7 mo). The 5-y BCR-free survival rate was 80.5% and 69.9% in the ePLND+SNB and ePLND groups, respectively. At multivariate analysis, prostate-specific antigen level, primary Gleason grade greater than 3, seminal vesicle invasion, and higher number of removed and positive nodes were independent predictors of BCR in the ePLND group. In the ePLND+SNB group, only the number of positive nodes was an independent predictor of BCR. The overall accuracy of the Memorial Sloan Kettering Cancer Center nomogram was higher in the ePLND+SNB than in the ePLND group. However, the nomogram was underestimating the probability of BCR-free status in the ePLND+SNB group, whereas the ePLND group was performing as predicted. Conclusion: Adding SNB to ePLND improves BCR-free survival, although the precise explanation of this observation remains speculative. Our results should be interpreted cautiously, given the nonrandomized nature and the selection bias of the study. © 2018 by the Society of Nuclear Medicine and Molecular Imaging.