Prostatic intraepithelial neoplasia (PIN) is the histologic lesion most strongly associated with prostate cancer and has been postulated to be a pre-malignant lesion. However, much of the natural history of PIN remains unknown. A more fundamental understanding of the relationship between PIN and invasive tumors at the molecular level is critically needed and represents an important future challenge for investigators. The importance of their recognition are based on the correlation between their presence and the existence of prostatic adenocarcinomas. It seemed significant to us to point out the criteria of the diagnosis and the action to be taken in front of the discovery of such lesions on biopsies in prostate sufferers.