Background: internal carotid intima thickness has been identified as a predictor of atherosclerosis. Patients with type ۱ diabetes are at risk for macrovascular complications. Atherosclerosis is ۲ to ۴ times more common in patients with diabetes, which exposes them to mortality and morbidity. The aim of this study was to determine the thickness of internal carotid intima thickness in children and adolescents with type ۱ diabetes and its relationship with cardiovascular risk factors in Iranian children and adolescents with type ۱ diabetes. Method: The present study is a cross-sectional study that was performed in Mofid and Imam Hossein hospitals in Tehran from ۲۰۲۰ to ۲۰۲۱. A total of ۹۱ patients with type ۱ diabetes in the age range of ۶-۱۸ years, who have been diagnosed with diabetes for at least three years, were included in the study as a diabetic group. Result: In total, ۹۱ children and adolescents with type ۱ diabetes were included in this study, of which ۴۴ (۴۸.۴%) were boys and ۴۷ (۵۱.۶%) were girls. The mean age of patients was ۱۲.۲۴ ± ۳.۱۷ and ranged from ۶ to ۱۸ years. The mean age of the patients at the time of diagnosis was ۵.۸۶ ± ۲.۹۸. In this study, blood pressure of ۶ patients (۶.۶%) was abnormal and the rest had normal blood pressure. In addition, the mean duration of disease in this study was ۶.۳ ± ۲.۵۷ years. The insulin of most patients (۹۳.۲%) was Analogue and only ۸.۸% of patients used Neutral Protamine Hagedorn (NPH) and Regular. The thickness of the intima of the right internal carotid artery is ۰.۵۴ ± ۰.۰۵ and the thickness of the intima of the left internal carotid artery is ۰.۴۸ ± ۰.۰۷. Conclusion: According to the results of this study, none of the factors of disease duration, age of onset, blood pressure, cholesterol, triglycerides, LDL (Low-Density Lipoprotein), HDL (High-Density Lipoprotein), HbA۱C (Hemoglobin A۱c), history of CHD (Coronary Heart Disease) and hyperlipidemia were significantly associated with the thickness of the intima of internal carotid artery. However, body mass index showed a significant relationship with the thickness of the left internal carotid intima.