To describe the clinical features of patients with childhood-onset myasthenia gravis (MG) (CMG) and explore predictors affecting the treatment outcomes.A retrospective observational cohort analysis of 859 patients with CMG with disease onset before age 14 years was performed at Tongji Hospital.Patients in the pubertal-onset group (n = 148) had a worse disease course than those in the prepubertal group (n = 711), including a higher incidence of generalized MG (GMG) at presentation, generalization of ocular MG (OMG), and more severe Myasthenia Gravis Foundation of America (MGFA) classification. All patients were initially treated with pyridostigmine, 657 with prednisone, and 196 with immunosuppressants (ISs). However, 226 patients were resistant to prednisone treatment. Multivariate analysis revealed that thymic hyperplasia, higher MGFA class, disease duration before prednisone administration, and thymectomy before prednisone administration were independent predictors of prednisone resistance. At the last visit, 121 of the 840 patients with OMG had developed GMG after a median of 10.0 years from symptom onset and 186 patients (21.7%) achieved complete stable remission (CSR). In multivariable analysis, age at onset, thymic hyperplasia, prednisone, and IS treatment were associated with generalization, whereas age at onset, disease duration, anti-acetylcholine receptor antibodies (AChR-ab), MGFA class II, short-term prednisone treatment, and IS treatment were associated with CSR.The majority of patients with CMG have mild clinical symptoms and favorable outcomes, especially those with earlier onset age, shorter disease duration, and negative AChR-ab. In addition, early prednisone and ISs are shown to be effective and safe for most patients with CMG.Copyright © 2023 Elsevier Inc. All rights reserved.