BACKGROUND AND OBJECTIVES: This study is to prospectively compare and analyze the aerodynamic changes in the patients with thyroid cancer before and after surgery. Changes in vocal function before and after thyroidectomy were examined using aerodynamic and related assessments. MATERIALS AND METHODS: Twenty one patients were evaluated preoperatively, 5-7 days and 6-7 weeks postoperatively to assess aerodynamic outcomes after thyroidectomy. Glottal input power (GIP), glottal efficiency (GE) and maximum phonation time (MPT), were determined the time of before surgery, 5-7 days after surgery and 6-7 weeks after surgery. RESULTS: According to the comparison analysis of the three periods, GIP with /pi/ phonation was significantly reduced at time of 5-7 days and 6-7 weeks after surgery, but not in the /p(h)i /and /p'i/ phonations. GE was significantly reduced in the /pi/, /p(h)i/ and /p'i/ phonations at time of 5-7 days and 6-7 weeks after surgery. MPT was significantly reduced at time of 5-7 days after surgery significantly. CONCLUSION: Aerodynamic assessment showed systematic changes in vocal function associated with thyroidectomy. These results should be useful data for vocal management in individuals who have had thyroidectomy and for assessment of voice disorders in clinical settings.