We compared the efficacy and side effects of propacetamol (P), an injectable prodrug of acetaminophen, 2 g and tramadol (T), a weak synthetic opioid, 1.5 mg.kg-1, given intravenously following thyroidectomy. 80 patients were randomly assigned to blindly receive one dose of P or T on request in the PACU. Residual pain was treated with i.v. PCA morphine. Pain and patient satisfaction were assessed with Visual Analog Scales. Demographic and peroperative data were comparable in both groups. Although the morphine consumption was comparable (p = 0.71), the decrease in VAS pain scores was significantly higher following tramadol (p = 0.03). More patients complained of nausea and vomiting (p = 0.01) during the first two hours following injection of tramadol, but there was no difference throughout the whole study. Oversedation was not observed in any group. We conclude that a single dose of tramadol provides a better quality of analgesia than propacetamol during the first six hours after thyroidectomy, but fails to ensure optimal analgesia, since VAS pain scores failed to fall below 3 despite the use of supplemental morphine.