Type 1 diabetes mellitus (T1DM) is the most common diabetes type among children, causing more than 90% of all cases of diabetes. It is one of the most common chronic diseases in childhood. T1DM can develop anytime during childhood, even during infancy, but it usually begins between age 4 years - 6 years and between age 10 years – 14 years. Symptoms are special, polyuria, polydipsia, polyphagia (3p) and weight loss. Treatment is complex, insulin replacement is necessary, diet, sport and mental health is important