['We determined the proportion of men with nonprogressive prostate cancer on active surveillance who had a trigger for treatment using various measures of prostate specific antigen kinetics.', 'A prospective phase II study of patients with favorable clinical parameters (stage T1b-T2b N0M0, Gleason sum 7 or less, prostate specific antigen 15 ng/ml or less) on active surveillance was initiated in 1995. Those patients considered at high risk for progression were offered radical intervention. The remaining patients were closely monitored and formed the cohort for this study. We calculated the proportion and frequency of patients who had a trigger for treatment based on the various prostate specific antigen triggers (prostate specific antigen doubling time, prostate specific antigen velocity, prostate specific antigen threshold).', 'Of 450 patients followed on surveillance 305 remained on active surveillance without definitive intervention. None of these 305 patients have died of prostate cancer or have had symptomatic metastatic disease develop. Median followup was 6.8 years. The proportion of patients who would have had a trigger for treatment ranged from 14% to 42% for the threshold triggers, 37% to 50% for the prostate specific antigen doubling time triggers and 42% to 84% for the velocity triggers.'] Does comparing prostate specific antigen trigger for intervention in men with stable prostate cancer on active surveillance?