Background: LHRH agonists (LHRHa) are commonly combined with radiotherapy in the neoadjuvant, concurrent, and adjuvant setting. Testosterone escape (TTE) (>1.74 nmol/L or >50 ng/dL) during therapy with LHRHa has been described, but the incidence and impact of TTE on outcome in this patient group needs to be characterized further. Methods: We performed a retrospective review of a database used for clinical outcomes and research ethics board approved studies, including chart audit of select patients (pts) where information was missing. To be included in the study, there had to be information on: 1) type of LHRHa, date of initiation, date of cessation, or duration of therapy and 2) radiotherapy information, with at least 6 months of follow-up after radiotherapy, 3) had to have radiotherapy to the prostate or prostate bed, and 4) had to have a least one testosterone- (TT) and prostatic-specific antigen (PSA) measurement. Results: 670 pts had a start date for androgen deprivation therapy (ADT) in the database. 630 pts had received an LHRHa, 560 pts had a start date for radiotherapy. 375 pts had sufficient information on ADT, radiotherapy, TT, and PSA levels, and 361 of these patients had information regarding their LHRHa. Median follow-up of patients still alive is 4.7 years. The median duration of LHRHa was 2.02 years. The median number of testosterone measurements per patient was 6. The incidence of TTE per patient course of treatment was: buserelin 9.3%; goserelin 10.5%; leuprolide IM 11.5%; leuprolide sc 23.9%; triptorelin 6.7% (p=0.02). Biochemical failure was defined as per the "nadir +2" definition, or at a value > 0.2 in those patients having had previous radical prostatectomy. There was no significant difference in either biochemical failure-free survival or overall survival in patients who experienced TTE versus those who did not. The most common PSA level during a TTE was an undetectable PSA. Conclusions: Even though there appears to be no impact of TTE on either biochemical relapse-free survival or overall survival, this study demonstrates that a rising PSA does not rule out TTE. Longer-term follow-up is planned.