Radiotherapy is a curative treatment for localized prostate cancer in its modalities of brachytherapy (BT) and external beam radiotherapy (EBRT). A temporary increase in prostate- specific antigen (PSA) values following a radiotherapy treatment coupled with a decrease without therapeutic intervention may happen in 30% of the patients. This phenomenon is known as PSA bounce and lacks prognostic effect in relation to tumor control. Additionally, it produces anxiety in the patient because of the fear of failure, and in the physicists due to the uncertainty about the state of the tumor. The etiology and pathogenesis are still unknown. Several factors associated with the tumor and the treatments have been evaluated in the studies which analyze this phenomenon, the age is the only observed factor with the highest consistency as a bounce predictor. The definition of biologic failure (BF) after EBRT or BT with or without androgenic deprivation (ADT) according to Phoenix criteria, which considers an increase of at least 2 ng/ml over PSA nadir, enables better taking the bounce phenomenon into account, although is not free from false BF that may affect to the relapse-free survival in patients with follow-up shorter than 3 years.