Neutrophil-to-lymphocyte ratio has been shown to be a prognostic factor in a number of different cancers. This is one of the largest studies to date to evaluate its effect on overall survival in patients who have undergone radical prostatectomy (RP) for localised prostate cancer. Those who received neoadjuvant or adjuvant treatment were excluded. Two thousand and sixty-seven patients who underwent RP over a 10-year period were retrospectively reviewed with a median follow-up time of 78 months. NLR ≥1.76 was deemed high. Patients with a high NLR were slightly older than the low NLR group (67 vs. 65 years old) and had a lower body mass index (BMI). Kaplan-Meier analysis demonstrated that a high NLR was associated with decreased cancer-specific survival and overall survival. There was no association with biochemical recurrence-free survival, although this has been demonstrated in other studies. The mechanism behind this trend is thought to be related to increased neutrophil-dependent inflammation and decreased lymphocyte-mediated tumour response. This study adds to the growing body of evidence that supports the use of NLR as a preoperative risk assessment of patients undergoing RP for localised prostate cancer.