Due to a high prevalence of diabetes in the population, the probability of orthodontic treatment of diabetic patients is also a very high. In particular it concerns type 1 diabetes occurring in children and adolescents, who most frequently undergo orthodontic treatment. In recent years, due to a wish to improve the aesthetics of the face, as well as due to prothetic and periodontal indications, orthodontic treatment becomes increasingly popular in adults. An orthodontist may come across patients with undiagnosed diabetes and unaware of their disease. It seems necessary for orthodontists to acquire knowledge on diabetes, its general symptoms, as well as topical ones, involving the oral cavity, and on appropriate procedures to be followed in emergency conditions occurring in those patients.Orthodontic treatment should be started only in patients with a stabilized blood glucose level. Otherwise, after applying orthodontic forces, an orthodontist may expect increased bone resorption, accelerated tooth movement and the absence of bone apposition on the unloaded side. Patients in whom the disease appears before the growth spurt are expected to show less bone growth, which may force modifications in the treatment plan. Patients with controlled diabetes usually do not require other methods of orthodontic treatment than healthy ones. It should be remembered that periodontitis, very frequently occurring in diabetic patients, might additionally contribute to the damage of periodontal tissues. Therefore, a regular cooperation with a diabetologist and periodontist is necessary during orthodontic treatment.