Pathogenesis of diabetes and its complications brings cluster of metabolic, hormonal, immunological and inflammatory changes starting in the very early stage of the disease. New data are available from the recent research on regulatory mechanisms involved in development of impaired glucose homeostasis as well as on the tissue damage. Several biomarkers like miRNAs or siRNAs open new possibilities for earlier diagnosis, prognosis and effective treatment. They elucidate in more detail our understanding of many processes including oxidative stress and their consequences in microvascular and macrovascular beds. The early and effective treatment may prevent these vascular changes which can be evaluated by novel and sensitive markers. The roles of genetic and epigenetic backgrounds are demonstrated as important factors modifying the results of treatment. However, intensive and causal treatment based on the recognized pathological processes confirms clinical benefits of the patients.