Diabetes mellitus is a disease characterized by an elevated level of glucose in the blood. This disease is divided into type 1 and type 2 diabetes, gestational diabetes and maturity-onset diabetes in the young, less common forms associated with infections, drugs and pancreatic disease. The main risk factors for diabetes mellitus are an individual's lifestyle and genetic predisposition. Diabetes develops due to an imbalance or complete cessation of functioning of the beta cell of the islets of Langerhans in the pancreas, which is the cause of a partial or complete cessation of insulin secretion. The diagnosis is based on characteristic clinical symptoms and is confirmed by fasting blood sugar analysis or oral glucose tolerance test. Treatment of diabetes is demanding and aims to achieve control over the disease. Primarily, the first step in treatment is education, which is carried out in the framework of patients suffering from diabetes. It is very important to teach patients how to control their diet, explain to them the importance of regular exercise and how to monitor their own blood glucose values. Patients have good results if they are monitored regularly. Treatment od diabetes is lifelong so it is important to be a great support to the patient and help him get help.