Evidence about the effectiveness of the N-methyl-D-aspartate antagonist ketamine to reduce postoperative acute and long-lasting pain is inconclusive. The aim of this study was to investigate effects of adding an intraoperative, pre-incision single intravenous dose of ketamine to a routine anaesthesia regimen on postoperative analgesic requirements, side-effects and persisting pain up to three months. After obtaining Ethical Committee approval and written informed patient consent, 120 patients were included in this prospective, randomised, double-blinded, placebo-controlled study. Patients were randomised into three groups, receiving 0.15 mg/kg ketamine intravenously, 0.5 mg/kg ketamine intravenously or normal saline in groups low-dose ketamine, moderate-dose ketamine and placebo, respectively. Anaesthesia maintenance, intraoperative pain management and postoperative pain therapy were standardised. The primary study endpoint was consumption of morphine during the first 24 hours after surgery. Three months after surgery, pain scores were assessed. Data were compared by t-test and Kruskall-Wallis test with alpha = 0.05. There was no difference between the groups in the assessed variables. These findings indicate that with the anaesthesia regimen described, and in the doses used, a single intravenous dose of ketamine does not reduce postoperative analgesic requirement or postoperative pain at three months.