Antithyroid drugs (ATDs) remain the first-line therapy in patients with Graves' disease (GD), despite a high relapse rate. The purpose of this study was to identify the predictors of remission in patients with GD treated with ATDs-retrospective study at an endocrine referral service in Northern Greece. Two-hundred and eleven patients met the study's criteria. Females (p = 0.049), non-smokers (p = 0.017), patients without ophthalmopathy (p = 0.033), and those developing pharmaceutical hypothyroidism (p = 0.018) experienced longer duration of remission. Duration of remission was positively associated with therapy duration (r (s) = 0.151, p = 0.030), maximum TSH levels during (r (s) = 0.241, p = 0.001), at the end (r (s) = 0.280, p < 0.001) and 3 months after therapy (r (s) = 0.341, p = 0.003). There was a negative association with free T4 (FT4) (r (s) = -0.426, p < 0.001) and free triiodothyronine (FT3) (r (s) = -0.467, p = 0.038) levels at 6 months after ATDs discontinuation. In multiple-regression analysis, only duration of the first ATDs course for more than 24 months independently predicted duration of remission. Female gender, non-smoking, the absence of orbitopathy, treatment duration, pharmaceutical hypothyroidism, higher TSH levels during, at the end and 3 months after ATDs discontinuation, and lower FT4 and FT3 levels 6 months after therapy were associated with longer duration of remission. However, only duration of ATDs therapy for more than 24 months independently predicted predict long-term remission in GD.