Increase of the Prostatic Specific Antigen (PSA) is a non-invasive, sensitive and specific markers for prostatic diseases, including prostatic cancer. However, age-related Benign Prostatic Hyperplasia (BPH), as well as prostatitis, may at the same time alter PSA values. The aim of this study was to evaluate the relationship between ageing and PSA, and whether age-specific upper normal limits of PSA should be considered for elderly patients. We evaluated 569 consecutive subjects aged 60 years or more (mean age 74.2 years) who were free from malignant prostatic disease, without clinical evidence of prostatic phlogosis and who were not receiving PSA levels affecting drugs. All patients underwent Digital Rectal Examination (DRE) and Trans-Rectal Ultrasonography (TRU), with determination of the three prostatic diameters, the Maximum Adenoma Diameter (MAD) and calculation of the prostatic volume (PV) by the ellipsoid formula. PSA was determined in all patients before DRE and TRU, and the PSA free ratio was determined in those with total PSA values >4 ng/ml. The PSA density was calculated according to the formula PSA/PV. One hundred and seventy-nine subjects (31.6%) were found to have PSA values >4 ng/ml: among them, 26 (14.5%) had values exceeding 10 ng/ml. Age was slightly correlated with PV (P<0.05), but not with PSA values. On the contrary, PSA values were strongly related with PV and MAD (P<0.01 both). Mean PSA-free ratio was 16.3+/-6.0% and most of patients had values in the so-called 'grey zone' of discrimination between benignity and malignity. Elevated PSA levels are common in older subjects without evidence of prostatic malignancy; PSA values are poorly affected by age itself and strongly correlated with increasing PV. These results suggest the possibility to consider as indicative of benignity PSA values between 4 and 10 ng/ml, when these values are associated with relevant increase of PV and with PSA-free ratio greater than 10%.