Objective: Postanaesthetic shivering is a recognised complication of general and regional anaesthesia. Pharmacological and nonpharmacological methods have been used to prevent shivering. This study was conducted to determine the efficacy of ketamine when compared with pethidine and placebo for the prevention of postanaesthetic shivering.Design: A randomised, double-blind study was conducted.Setting and subjects: This study was conducted on 90 American Society of Anesthesiologists (ASA) I and II patients of both genders, aged 18-70 years, who were to undergo surgery under general anaesthesia. Patients were randomised into three equal groups: Group S received a saline placebo, Group P received pethidine 20 mg and Group K received ketamine 0.5 mg/ kg. The study medication was given within 20 minutes of the estimated end of surgery.Outcome measures: Haemodynamic parameters were noted before, during and after anaesthesia. Tympanic temperature was recorded during the intraoperative period, on arrival in the recovery room (T0) and subsequently at 10 minutes (T10), 20 minutes (T20) and 30 minutes (T30). Shivering was graded on a four-point scale. Pain was assessed and recorded by means of a visual analogue scale. Any untoward side-effects were also noted. Results:The demographic profile of the patients was similar. The number of patients shivering at T0 and subsequently at T10 and T20 was significantly less in Group K and Group P than in Group S (p-value < 0.005). However, there was no difference between Group P and Group K (p-value > 0.005). Thirty minutes after the end of the anaesthetic, there was no difference between the groups (p-value > 0.005). Haemodynamic parameters were similar throughout. The incidence of adverse effects was similar. Conclusion:Ketamine was found to be as effective as pethidine in preventing postanaesthetic shivering without increasing the risk of side-effects.