Background: During thyroid lobectomy, division of the thyroid parenchyma has traditionally been accomplished using suture ligation. Development of hemostatic techniques in the forms of ultrasonic dissection (UD) and electronic vessel sealing (EVS) have increased the usage of these devices during thyroid operations. We sought to characterize the thermal profile of each of these devices when used to divide the parenchyma of the thyroid gland. Methods: Using a porcine model, the parenchyma of the gland was sealed by alternating application of the UD and EVS devices. In each case, the thermal activity was recorded using infrared thermal imaging. We performed multiple seals with each instrument and then compared the thermal profiles. Results: There was no significant difference in lateral thermal spread of EVS and UD above 39, 40 or 60°C (2.30 ± 0.31mm versus 2.53 ± 0.47 mm, P = 0.26; 2.22 ± 0.27 mm versus 2.47 ± 0.47mm, P = 0.22, and 1.37 ± 0.27 mm versus 1.54 ± 0.26 mm, P = 0.22). There was no significant difference in mean time above 39 or 40°C (35.1 ± 8.7 s versus 31.7 ± 9.3 s, P = 0.47 and 29.9 ± 8.1 s versus 27.3 ± 6.7 s, P = 0.50). UD reached a greater maximum temperature (179.12 ± 0.0008C versus 96.52 ± 5.6C, P ≤ 0.001) and stayed over 60°C for longer than EVS (9.5 ± 1.8 s versus 5.3 ± 0.97, P ≤ 0.001). Conclusions: The amount of lateral spread of thermal energy was not significantly different between the UD and EVS devices. However, the use of UD produced a higher maximum temperature during thyroid parenchyma sealing and remained above 60°C longer than EVS. This may translate into greater thermal injury to thyroid and surrounding tissues during division. © 2011 Elsevier Inc. All rights reserved.