['To evaluate prostate-specific antigen (PSA) spikes after permanent prostate brachytherapy in low-risk patients.', 'The study population consisted of 164 prostate cancer patients who were part of a prospective randomized trial comparing (103)Pd and (125)I for low-risk disease. Of the 164 patients, 61 (37.2%) received short-course androgen deprivation therapy. The median follow-up was 5.4 years. On average, 11.1 post-treatment PSA measurements were obtained per patient. Biochemical disease-free survival was defined as a PSA level of < or =0.40 ng/mL after nadir. A PSA spike was defined as an increase of > or =0.2 ng/mL, followed by a durable decline to prespike levels. Multiple parameters were evaluated as predictors for a PSA spike.', 'Of the 164 patients, 44 (26.9%) developed a PSA spike. Of the 46 hormone-naive (125)I patients and 57 hormone-naive (103)Pd patients, 21 (45.7%) and 8 (14.0%) developed a PSA spike. In the hormone-naive patients, the mean time between implantation and the spike was 22.6 months and 18.7 months for (125)I and (103)Pd, respectively. In patients receiving neoadjuvant androgen deprivation therapy, the incidence of spikes was comparable between isotopes ((125)I 28.1% and (103)Pd 20.7%). The incidence of spikes was substantially different in patients <65 years vs. > or =65 years old (38.5% vs. 16.3%). On multivariate Cox regression analysis, patient age (p < 0.001) and isotope (p = 0.002) were significant predictors for spike.'] Do isotope and patient age predict for PSA spikes after permanent prostate brachytherapy?