Summary: Diabetes mellitus remains one of the most common chronic disorders. The majority of patients are diagnosed with type 2 diabetes (ca. 90%) or type 1 diabetes (ca. 5-10%). Other types of diabetes remain rare. Diagnosis is usually based on a clinical examination and biochemical results. Some patients simultaneously demonstrate characteristic features of both main types of diabetes. This can produce difficulties in diagnosis. Latent autoimmune diabetes in adults (LADA) is a complex autoimmune form of type 1 diabetes. This type of diabetes is often misdiagnosed and treated as type 2 diabetes. Proper diagnosis of the type of diabetes is vital for introducing the optimal therapy.