Background: A key concern among patients who undergo thyroid surgery is postoperative weight gain. Yet, the impact of thyroid surgery on weight is unclear. Methods: The population-based Rochester Epidemiology Project was used to examine weight and body mass index (BMI) changes at one, two, and three years of follow-up in (i) patients with thyroid cancer and benign thyroid nodules after thyroid surgery, and (ii) patients with thyroid nodules who did not have surgery. A comprehensive systematic review of the published literature from inception to February 2016 was also conducted. The results were pooled across studies using a random effects model. Results: A total of 435 patients were identified: 181 patients with thyroid cancer who underwent surgery (group A), 226 patients with benign thyroid nodules without surgery (group B), and 28 patients with benign thyroid nodules undergoing surgery (group C). Small changes in mean weight, BMI, and the number of patients whose weight increased between 5 and 10 kg were similar during each year of follow-up between patients in groups A and B. Furthermore, age >50 years, female sex, baseline BMI >25 kg/m2, and thyrotropin value at one to two years were not predictors of a 5% weight change. In the meta-analysis, 11 studies were included. One to two years after surgery for thyroid cancer or thyroid nodules, patients gained on average 0.94 kg [confidence interval (CI) 0.58-1.33] and 1.07 kg [CI 0.26-1.87], respectively. Patients with benign thyroid nodules who did not have surgery gained 1.50 kg [CI 0.60-2.4] at the longest follow-up. Conclusions: On average, patients receiving care for thyroid nodules or cancer gain weight, but existing evidence suggests that surgery for these conditions does not contribute significantly to further weight gain. Clinicians and patients can use this information to discuss what to expect after thyroid surgery.