Background: The long-term outcomes of first-line choice among ATD, RAI, and thyroidectomy for GD patients remain unclear., Objective: To compare the long-term morbidity, mortality, relapse, and costs of GD patients receiving first-line treatment., Methods: A population-based retrospective cohort of GD patients initiating first-line treatment with ATD, RAI, or thyroidectomy as a first-line primary treatment between 2006 and 2018 from Hong Kong Hospital Authority was analyzed. Risks of all-cause mortality, CVD, AF, psychological disease, diabetes, and hypertension were estimated using Cox proportional hazards regression models. The 10-year healthcare costs, change of comorbidities, and risk of relapse were compared across treatments., Results: Over a median follow-up of 90 months with 47,470 person-years, 6385 patients (ATD, 74.93%; RAI, 19.95%; thyroidectomy, 5.12%) who received first-line treatment for GD were analyzed. Compared with ATD group, patients who had undergone surgery had significantly lower risks of all-cause mortality [hazard ratio (HR) = 0.363, 95% confidence interval (CI) = 0.332-0.396], CVD (HR = 0.216, 95% CI = 0.195-0.239), AF (HR = 0.103, 95% CI = 0.085-0.124), psychological disease (HR = 0.279, 95% CI = 0.258-0.301), diabetes (HR = 0.341, 95% CI = 0.305-0.381), and hypertension (HR = 0.673, 95% CI = 0.632-0.718). Meanwhile, RAI group was also associated with decreased risks of all-cause mortality (HR = 0.931, 95% CI = 0.882-0.982), CVD (HR = 0.784, 95% CI = 0.742-0.828), AF (HR = 0.622, 95% CI = 0.578-0.67), and psychological disease (HR = 0.895, 95% CI = 0.855-0.937). The relapse rate was 2.41% in surgery, 75.60% in ATD, and 19.53% in RAI group. The surgery group was observed with a significant lower Charlson Comorbidity Index score than the other 2 groups at the tenth-year follow-up. The mean 10-year cumulative healthcare costs in ATD, RAI, and surgery group was US$23915, US$24260, and US$20202, respectively., Conclusions: GD patients who received surgery as an initial treatment appeared to have lower chances of all-cause mortality, CVD, AF, psychological disease, diabetes, and hypertension in the long-term when compared to those treated with ATD or RAI. The surgery group had the lowest relapse and direct healthcare costs among the 3 treatment modalities. This long-term cohort study suggested surgery may have a larger role to play as an initial treatment for GD patients., Competing Interests: The authors report no conflicts of interest., (Copyright © 2021 The Author(s). Published by Wolters Kluwer Health, Inc.)