OBJECTIVE Preoperative staging of patients diagnosed with prostate cancer is vital in determining the correct treatment including radical prostatectomy. Serum prostate-specific antigen (PSA), Gleason score in prostate biopsies and predicted clinical T-stage using digital rectal examination and transrectal ultrasound are known predictors of extraprostatic disease after surgery. This study analysed whether the percentage of positive biopsy cores was a significant preoperative predictor of extraprostatic disease in patients undergoing radical prostatectomy. MATERIAL AND METHODS An analysis was conducted on 390 consecutive patients who underwent radical prostatectomy at Arhus University hospital from 2000 to 2006. Serum PSA, Gleason score, predicted clinical T-stage and percentage of positive biopsy cores were tested in a univariate analysis, and then a multivariate logistical regression model, to determine whether they were predictors of extraprostatic disease. RESULTS The percentage of positive biopsy cores was, together with T-stage and Gleason score, shown to be a significant predictor of extraprostatic disease in both univariate and multivariate analysis with a p-value of 0.05. The calculation yields a model that can predict risk of non-organ-confined disease in a non-screened population. CONCLUSION Being an independent predictor of extraprostatic disease, the percentage of positive biopsy cores can supplement existing preoperative staging variables as found in current staging nomograms.