The Authors observed a group of 20 patients, each of them suffering from prostatic carcinoma clinically localized in only one lobe. All patients were investigated by trans-rectal US tomography, performed with a 5 MHz linear sound, and by prostatic biopsy in both lobes. The Authors evaluate US tomography results in comparison with biopsy executed on the apparently normal lobe and appreciable sensibility, specificity and predictive capability of this method. The Authors believe that trans-rectal US tomography, after having considered sensitivity and specificity values is not to propose as a screening method for early diagnosis of prostatic carcinoma.