Abstract Aims We aimed to analyze the relationship between epilepsy and glutamic acid decarboxylase autoantibodies (GADA) in patients with type 1 diabetes mellitus (T1DM) and the impact of GADA on demographic, clinical, and metabolic data in T1DM patients with epilepsy. Methods We searched for patients with T1DM ≤20 years and GADA measurements, and within this group for patients with epilepsy. We formed groups: T1DM + Epilepsy + GADA positive; T1DM + Epilepsy + GADA negative; T1DM + GADA positive; T1DM + GADA negative. We used logistic regression to analyze the relationship between epilepsy and GADA with odds ratio adjusted for sex, duration of diabetes (DOD), and age at diabetes onset (ADO). We used logistic regression with odds ratio adjusted for DOD and ADO onset using epilepsy as a dependent variable and GADA, HbA1c, ketoacidosis, severe hypoglycemia (SH), sex, celiac disease, and autoimmune thyroiditis as independent variables. We conducted regression analyses adjusted for sex, DOD, and ADO to analyze ...