Monitoring the evolution of prostate cancer has crucial importance since this tip of neoplasia has a variable biology, ranging from latent cancers to extremely aggressive tumors. At the moment, PSA (prostate specific antigen) values point out to either successful or unsuccessful prostate cancer therapy. Depending on therapeutic strategies, biochemical recurrence (BCR) is differently defined. After radical prostatectomy, the PSA declines to undetectable levels in 3-4 weeks; BCR: PSA = 0.2-0.5 ng/mL for a single measurement or two consecutive values which surpass 0,2-0,4 ng/mL. PSADT < 10 months is a predictor for the progression of the disease. After external beam therapy, PSA is slowly decreasing reaching up the nadir of 0.2-0.5 ng/mL in months or years; BCR: PSA = nadir + 2 ng/mL. In the case of brachytherapy, the nadir is reached in 2-4 years; BCR: nadir + 2 ng/mL. After hormonal therapy, PSA declines in 3-6 months, maintains low values for 18-24 months, then increases, settling for hormone independency. After chemotherapy, PSA is considered normal at values < 2 ng/mL; the response of PSA represents a confirmed decreasing from the second test at 4 or more weeks after the initial decline; the length of the response is the period between first decline with 50 % of PSA to 50 % increase from nadir; the progression of PSA is shown in the increase with 25 % in comparison to the basic level. In the case of active monitoring, a PSADT < 2 years is an indication for radical prostatectomy, but there are cancers which can evoluate despite a stable PSA. The "PSA bounce" phenomenon and the "PSA surge postchimiotherapie" syndrome can complicate the assessment of biochemical recurrence.