Background: We sought to ascertain whether there is an association between prostate cancer (PC)-specific mortality (PCSM) and salvage androgen deprivation therapy (ADT) timing amongst men with short versus long prostate-specific antigen doubling times (PSA-DT)s. Methods: The study cohort was selected from 206 men with localized unfavorable-risk PC who were randomized to radiation therapy (RT) or RT plus 6 months of ADT between 1995 and 2001. Fifty-four men who received salvage ADT for PSA failure after a median follow up of 18.72 years following randomization defined the study cohort. Fine-Gray competing risks regression analyzed whether the timing of salvage ADT was associated with an increased risk of PCSM after adjusting for age, comorbidity, known PC prognostic factors, and previously identified interactions. Results: After a median follow-up of 5.68 years (IQR 3.05 - 9.56) following salvage ADT 49 of the 54 men (91%) died, 27 from PC (54% of deaths). Increasing PSA-DT as a continuous covariate was associated with a decreasing risk of PCSM (adjusted hazard ratio [AHR] 0.33, 95% CI 0.13, 0.82; P=0.02). Amongst men with a long PSA-DT (≥6 months), initiating salvage ADT later (PSA>12ng/mL, upper quartile) versus earlier was associated with an increased risk of PCSM (AHR 8.84, 95% CI 1.99-39.27; P=0.004); whereas for men with a short (<6 months) PSA-DT (AHR 1.16, 95% CI 0.38-3.54; P=0.79) this was not true. Conclusions: Early initiation of salvage ADT for post-RT PSA recurrence in men with a PSA-DT of 6 months or more may reduce the risk of PCSM, arguing against the unproven assumption that patients with a short PSA-DT are those most likely to benefit from early initiation of salvage ADT. Clinical trial information: NCT00116220