BACKGROUND: During thyroidectomy, the patient's neck is fully extended for good surgical exposure. After thyroidectomy, patients usually complain of posterior headache and posterior neck pain. It has been known that the greater occipital nerve block is a means of effective medical treatment for occipital headache and posterior neck pain. Therefore, we examined the effects of a greater occipital nerve block on postthyroidectomy headache and neck pain. METHODS: This study was randomized and double-blinded. After anesthesia induction, patients were administered greater occipital nerve block by the same anesthesiologist; 0.25% bupivacaine 5 ml was used for each greater occipital nerve block. Patients in the control group did not receive a greater occipital nerve block. After thyroidectomy, another anesthesiologist evaluated patients' headaches and neck pains at 4, 12, and 24 hours postoperatively by using a VAS. RESULTS: Forty four patients were included. The number of patients in the control and the block group were 27 and 17, respectively. VAS scores of occipital headache after 4, 12, and 24 hours in the control group were 3.52+/-2.75, 3.67+/-2.75, and 2.95+/-1.96, respectively. VAS scores of occipital headache after 4, 12, and 24 hours in the block group were 0.05+/-0.65, 0.50+/-0.85, and 0.43+/-0.64, respectively. VAS scores of posterior neck pain after 4, 12, and 24 hours in the control group were 4.09+/-2.79, 3.81+/-2.60, and 3.00+/-2.02. VAS scores of posterior neck pain after 4, 12, and 24 hours in the block group were 1.29+/-2.20, 1.00+/-1.66, and 0.79+/-1.25, respectively. The pain experienced by the block group was significantly lower than that of the control group. CONCLUSIONS: We conclude that greater occipital nerve block is an effective modality for reducing post-thyroidectomy headache and posterior neck pain.