The Gleason grading system is a powerful tool to prognosticate and aid in the treatment of men with prostate cancer. The needle biopsy Gleason score correlates with virtually all other pathological variables, including tumour volume and margin status in radical prostatectomy specimens, serum prostate-specific antigen levels and many molecular markers. The Gleason score assigned to the tumour at radical prostatectomy is the most powerful predictor of progression after radical prostatectomy. However, there are significant deficiencies in the practice of this grading system. Not only are there problems among practising pathologists but also a relative lack of interobserver reproducibility among experts.