Prostate carcinoma (PCa) exhibits a wide range of architectural and cytological features. Gleason grading remains as one of the most powerful histological prognostic parameters. However, it has evolved considerably. High-grade prostatic intraepithelial neoplasia (high-grade PIN) is accepted as a precursor lesion to PCa. Its detection in prostate biopsy is also considered as a risk factor for detecting cancer in subsequent biopsies. Such risk, however, has significantly decreased in recent studies. Intraductal carcinoma of the prostate (IDC-P) represents the intraductal spread of invasive cancer and constitutes a poor histologic parameter. This article reviews the key histological features of PCa, high-grade PIN and IDC-P, as well as the Gleason grading system that was most recently updated in 2005.