[en] Purpose: The significance of prostate-specific antigen (PSA) increases during the recovery of androgen after androgen deprivation therapy (ADT) and radiotherapy for prostate cancer is not well understood. This study sought to determine whether the initial PSA increase from undetectable after completion of all treatment predicts for eventual biochemical failure (BF). Methods and Materials: Between July 1992 and March 2004, 163 men with a Gleason score of 8-10 or initial PSA level >20 ng/mL, or Stage T3 prostate cancer were treated with radiotherapy (median dose, 76 Gy) and ADT and achieved an undetectable PSA level. The first detectable PSA level after the cessation of ADT was defined as the PSA sentinel rise (SR). A PSA-SR of >0.25, >0.5, >0.75, and >1.0 ng/mL was studied as predictors of BF (nadir plus 2 ng/mL). Cox proportional hazards models were used for univariate and multivariate analyses for BF adjusting for pretreatment differences in Gleason score, stage, PSA level (continuous), dose (continuous), and ADT duration (<12 vs. ≥12 months). Results: Of the 163 men, 41 had BF after therapy. The median time to BF was 25 months (range, 4-96). The 5-year BF rate stratified by a PSA-SR of ≤0.25 vs. >0.25 ng/mL was 28% vs. 43% (p = 0.02), ≤0.5 vs. >0.5 ng/mL was 30% vs. 56% (p = 0.0003), ≤0.75 vs. >0.75 ng/mL was 29% vs. 66% (p < 0.0001), and ≤1.0 vs. >1.0 ng/mL was 29% vs. 75% (p < 0.0001). All four PSA-SRs were independently predictive of BF on multivariate analysis. Conclusion: The PSA-SR predicts for BF. A PSA-SR of >0.5 ng/mL can be used for early identification of men at greater risk of BF