Objective: The purpose of this study was to determine how the timing of thyroidectomy influenced postoperative weight change. Methods: We conducted a two-institution study, identifying patients treated with total thyroidectomy for hyperthyroidism. Patients were classified as 'early' if they were referred for surgery as the first treatment option, or 'delayed' if they were previously treated with radioactive iodine (RAI). Groups were compared with the Student's t-test or χ 2 test where appropriate. Results: There were 204 patients undergoing thyroidectomy for hyperthyroidism. Of these, 171 patients were classified as early and 33 were classified as delayed. Overall, patients gained 6.0 % ±0.8 of their preoperative body weight at last follow-up. Preoperative body mass indexes (BMIs) were similar between groups (p = 0.98), and the median follow-up time was 388 days (range 15-1,584 days). Both groups gained weight until they achieved a normal thyroid-stimulating hormone (TSH) postoperatively. After achieving a normal TSH, the early group stabilized or lost weight (-0.2 lbs/day), while the delayed group continued to gain weight (0.02 lbs/day; p = 0.61). At last follow-up, there were significantly more patients in the delayed group who increased their BMI category compared with the early group (42.4 vs. 21.6 %; p = 0.01). Twice as many patients in the delayed group moved up or into an unhealthy BMI category (overweight or obese) compared with the early group (39.4 vs. 19.3 %; p = 0.01). Conclusions: Compared with patients initially treated with RAI, patients with hyperthyroidism who underwent surgery as the first treatment were less likely to become overweight or obese postoperatively. © 2014 Society of Surgical Oncology.