Serum PSA has been commercially available for more than ten years, and has proved to be the most important tumour marker for prostate cancer. We review the clinical usefulness and limitations of serum PSA as a tumour marker of prostate cancer.The international literature and medical databases were searched for studies on the contributions and limitations of PSA in clinical practice.Serum PSA > or = 4.0 ng/ml is commonly regarded as elevated, and give rise suspicion of prostate cancer. However, only one out of four men with serum PSA level between 4.0 ng/ml and 10.0 ng/ml has prostate cancer. The most common cause of elevated serum PSA value in this group is benign prostatic hyperplasia. In an attempt to increase the sensitivity as well as the specificity for serum PSA in the detection of prostate cancer, the serum PSA level has been combined with age of patients (age-specific serum PSA), time (PSA velocity), prostate volume (PSA density), different molecular PSA forms, like per cent of free PSA. Some of these new methods have shown promising results.PSA is the best and most widely used tumour marker in urology. However, it is important that clinicians know the limitations of this marker.