Introductıon Surgical principles established by the pioneers of thyroid, were good exposure of thyroid gland, clear identification of nerves, parathyroid glands and perfect heamostasis [1] . New vessel sealing technologies Ligasure (Covidien, Boulder, Colorado) and Harmonic Scalpel (Ethicon Endo-Surgery Inc, Cincinnati, Ohio) have emerged in the recent literature [2] [3] [4] . Harmonic Scalpel (HS) is a new promising tool introduced to surgery two decades ago. It uses high frequency (55,500 Hz)

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... mechanical energy to cut and coagulate tissues at the same time. Mechanism of HS depends on denaturation of protein by using ultrasonic vibration to transfer mechanical energy sufficient to break tertiary hyrogen bonds [5, 6] . Proposed advantages with its use include less thermal tissue damage to adjacent structures as compared with electrocautery and reduction in the operative time due to combination of simultaneous cutting and coagulation functions [7]. There have been several recent studies investigating the safety of HS in patients undergoing thyroidectomy [8] [9] [10] . Most studies conclude that use of HS decreases both operative time and intraoperative blood loss and provides benefits in postoperative pain without increasing complication rates when compared to conventional techniques [7] [8] [9] [10] [11] . The aim of this prospective randomized study is to evaluate the effect of HS on complications in dissection of left lower neck region and parathyroid glands and nerves (recurrent inferior laryngeal nerve, vagus, accessory, phrenic and hypoglossal) in patients with papillary thyroid carcinoma (PTC) undergoing central or lateral neck dissection. Abstract Aım: The aim of this study was to investigate whether Harmonic Scalpel (HS) increases the complication rate in the patients undergoing neck dissection in patients with Papillary Thyroid Carcinoma (PTC). Methods: 95 patients with PTC undergoing bilateral total thyroidectomy and central or lateral neck dissection were included in to study. Patients whom heamostasis was carried out using HS at each stage of the operation were classified as group I (n=52), and patients whom heamostasis was performed without HS in the dissection of nerves and in the dissection of regions containing parathyroids and ductus thoracicus as Group II (n=43). Groups were compared in terms of operation time, postoperative nerve injury, hypoparathyroidsm and development of chylous fistula. Results: Demographic data, stage of tumor and type of operation were similar between groups. Mean operation time was 19 min. shorter in group I (p=0.003). There was no difference in nerve injury and hypoparathyroidsm between groups. Chylous fistula was seen in 3(5.7%) patients in group I. It was not seen in group II. Conclusıon: Use of HS in patients with PTC undergoing neck dissection decreases operation time significantly without increasing the rate of nerve and parathyroid injury, but may increase the risk of development of chylous fistula.