Radical prostatectomy is an effective treatment for patients with clinically localized prostate cancer and is associated with a very low level of mortality. However, many men with untreated clinically localized prostate cancer do not die from the disease and, following radical prostatectomy, some patients will suffer from a loss of potency and/or incontinence. A major challenge faced by the clinician is to identify the individual patient who will benefit from radical prostatectomy. In this review, we discuss the natural history of clinically localized prostate cancer and the factors likely to affect the treatment decision for an individual patient. Recent studies by other investigators and ourselves have revealed that the T1/T2 tumour is heterogeneous with respect to pathological stage and outcome, and that the quantity of Gleason grade 4/5 tumour is a significant prognostic factor predicting lymph node progression and capsular penetration. Classification and Regression Trees (CART) analysis including such preoperative parameters can be used to predict the probability of an individual patient having a pT2 tumour and, therefore, whether he could have a nerve-sparing radical prostatectomy - a procedure which offers better outcomes in terms of potency and continence.