BACKGROUND: This study was performed to evaluate the effectiveness of intravenous low dose ketamine for reducing the incidence and severity of postoperative sore throat (POST). METHODS: This was a prospective, randomized, double-blind clinical trial. The study population consisted of 70 patients between 20 and 70 years old who were classified as American Society of Anesthesiologists I-II and were scheduled for elective laparoscopic cholecystectomy. The patients were divided randomly into two groups. Patients in the ketamine group received an intravenous injection of 0.5 mg/kg of ketamine just before induction, followed by 10 microg/kg/min throughout the operation. Patients in the control group received intravenous saline instead of ketamine. The patients were interviewed 1, 6, and 24 h after the operation. The incidence and severity of POST were recorded. RESULTS: No significant differences in the incidence and severity of POST during the 24 h after the operation were found between the two groups (21/31 in the ketamine group vs. 26/34 in the control group, P = 0.398). CONCLUSIONS: Intravenous injection of low dose ketamine was not effective for reducing POST.