For more than four decades the Gleason score is the most widely accepted histopathological grading system for prostate cancer. It is a 5-tier grading system that correlates with tumour differentiation and is solely based on architectural patterns within the tumour. Although robust over time, revision of Gleason grading became unavoidable as diagnosis and treatment of prostate cancer also underwent an enormous evolution over time. In 2005 the International Society of Urological Pathology (ISUP) proposed several modifications to the Gleason system which should keep this grading system timely. This review compares the original system to the modified Gleason system and especially focuses on the prognostic relevance of the modifications. It further deals with the question if the Gleason system will be able to keep its prominent role in the diagnostic and prognostic algorithm for prostate carcinoma, especially in the nearby molecular era. (BELG J MED ONCOL 2012;6:45–51)