The prostate specific antigen (PSA) has gained great importance for the diagnosis and the treatment of prostate carcinoma since its isolation from prostate tissue in 1979. PSA is produced and secreted almost only by the prostatic tissue. After radical prostatectomy PSA changes from a tissue specific marker to a tumor specific parameter. At least 30 days after radical prostatectomy the PSA serum level should decline nondetectable values. A high incidence for a local recurrence, distant metastases, or a incomplete resection of the prostate is a still present PSA serum value. After a radiation or androgen deprivation therapy the PSA value is a prognostic marker. A good prognosis can be expected if the PSA level decreases after androgen deprivation therapy to values below 4 ng/ml. In contrast to that increasing PSA levels indicate a local or distant recurrence. Progression of the tumor without an increase of PSA values is possible but rare. It could be shown in several studies, that the determination of PSA values is sufficient for routine treatment control and that other methods could therefore be omitted.