BACKGROUND: Tramadol is a centrally acting analgesic with weak opioid agonist properties and has effect on the spinal inhibition of pain. This study was designed to evaluate the efficacy of tramadol in the treatment of postanesthetic shivering. METHODS: Sixty patients (ASA class I/II) who showed postanesthetic shivering were randomly assigned into three groups (n=20): Normal saline group; normal saline 10 ml, tramadol (TRD) 0.5 mg/kg group; tramadol 0.5 mg/kg, TRD 1.0 mg/kg group; tramadol 1.0 mg/kg. And all patients received standard postoperative management in the recovery room. Evaluation of the grade of shivering was done at 30 seconds, 2, 5 and 10 minutes from the beginning of the treatment by the same investigator who had injected the drug. The age, sex, weight, duration of anesthesia and axillary temperature were recorded. RESULTS: By 30 seconds, 2 minutes, 5 minutes, and 10 minutes, 0, 4, 9, 9 patients of the 0.5 mg/kg tramadol group (n=20) and 7, 18, 19, 19 patients of the 1.0 mg/kg tramadol group (n=20) stopped the shivering respectively. But in 3 patients of 0.5 mg/kg tramadol group who stopped shivering by 5 minutes, shivering was recurred within 10 minutes and in 3 patients who had not stopped shivering by 5 minutes, shivering stopped by 10 minutes. In the placebo group, only 1 patient stopped shivering by 5 minutes. CONCLUSION: 1.0 mg/kg of tramadol was effective for the treatment of postanesthetic shivering but 0.5 mg/kg of tramadol was ineffective.