Background: Long-term health issues associated with type 1 diabetes mellitus (T1DM), such as renal impairment, retinal affection, as well as heart and neurological conditions, can have an impact on a patient's quality of life. The degree of control of diabetes and its complications are known to be directly correlated, and achieving optimal blood glucose levels lowers the risk of long-term complications. Objective: The aim of the present study is to evaluate the proportion of uncontrolled T1DM and factors that influence glycemic control in children and adolescents with T1DM in the Assiut Governorate of Egypt. Patients and methods: A total of 500 participants with TIDM for at least three years, ranging in age from 3 to 18 were recruited. We conducted a thorough history taking that covered sociodemographic factors, disease-related factors, disease management plans, and the level of patient disease knowledge. All study participants had their body mass indexes evaluated. We divided the study participants into two groups; those with controlled T1DM and those without, based on the glycosylated haemoglobin (HbA1c) targets. Results: The mean age was 13.56 (SD 3.49) years, and 52% of the study participants were female and 48% were males. Only 38% of participants lived in urban area, while 62% lived in rural area. Only16.8% of the studied diabetic children and adolescents had controlled T1DM while 83.2% had uncontrolled T1DM. Predictors for uncontrolled T1DM in children and adolescents were female gender, irregular treatment and poor level knowledge. Conclusion: Most of the diabetic children and teenagers in this study had uncontrolled T1DM. Poor knowledge about diabetes was the most risk factor for uncontrolled T1DM. Health education programs for T1DM patients are needed to achieve good glycemic control.