Background: The aim of this study was to compare the efficacy of ketorolac, paracetamol, and paracetamol plus morphine on pain relief after thyroidectomy. Methods: Eighty patients were randomly allocated to one of the 4 groups: normal saline (group C), ketorolac 30 mg (group K), paracetamol 1 g (group P), and paracetamol 700 mg plus morphine 3 mg (group PM). Each regimen was administered intravenously (IV) 30 min. before the end of surgery. If pain was not relieved, patients received an IV bolus of pethidine hydrochloride 25 mg. Pain intensity using a visual analogue scale (VAS) was recorded at 0.5, 1, 2, 4, and 6 hr after the end of surgery. Results: VAS at 0.5 and 1 hr after the end of surgery were significantly lower in group K, group P, and group PM than in group C (P < 0.05). The number of patients receiving pethidine hydrochloride at 0.5 and 1 hr after the end of surgery was significantly lower in group K, group P, and group PM than in group C (P < 0.05). There was no significant difference among the groups in the incidences of adverse events associated with study medications and patient satisfaction (P > 0.05). Conclusions: Paracetamol 1 g IV possesses a similar analgesic efficacy to ketorolac 30 mg IV after thyroidectomy. Paracetamol may represent an alternative to ketorolac for pain prevention after mildly to moderately painful surgery in situations where the use of NSAIDs is unsuitable.