OBJECTIVE To determine whether increasing body mass index (BMI) is associated with more aggressive disease and adverse surgical outcomes in patients with papillary thyroid cancer (PTC). DESIGN Retrospective review of a prospective database. SETTING Single academic tertiary care center. PATIENTS A total of 443 patients older than 18 years who underwent total thyroidectomy for PTC from January 1, 2004, through March 31, 2011, were included in the analysis. Patients were organized into 4 BMI (calculated as weight in kilograms divided by height in meters squared) groups: normal (18.5-24.9), overweight (25-29.9), obese (30-39.9), and morbidly obese (≥40). MAIN OUTCOME MEASURES Disease stage at presentation, histologic subtype, duration of anesthetic induction and extubation, duration of surgery, surgical complications, length of hospital stay, and American Society of Anesthesiologists (ASA) class. RESULTS Ages ranged from 18 to 89 years. Greater BMI was associated with more advanced disease stage at presentation (P < .001) and more aggressive PTC histopathologic subtype (P = .03). Morbidly obese patients presented more frequently with stage III or IV disease (odds ratio, 3.67; P < .001). Greater BMI was also associated with longer duration of anesthetic induction (P < .001), increased length of stay (P < .001), and higher ASA class (P < .001). Duration of surgery was not associated with BMI. There was a trend toward larger tumors with increasing BMI (P = .06). Obese BMI was associated with more preoperative vocal cord paralysis due to local invasion (odds ratio, 9.21; P = .001). CONCLUSIONS Obese patients present with more advanced stage and more aggressive forms of PTC. This finding suggests that obese patients should be screened for thyroid cancer.