Gestational diabetes mellitus (GDM) is a heterogeneous entity, including carbohydrate intolerance of variable severity with onset or first recognition during pregnancy. Insulin resistance and beta-cell dysfunction are thought to be major determinants of its development. Its pathomechanism in many ways resembles that of type 2 diabetes. There is an evolving body of evidence from the last decade presenting similarities between gestational diabetes and the metabolic (insulin resistance) syndrome. These new observations suggest that GDM might be an early manifestation of the metabolic syndrome. The desired treatment target of GDM is normoglycemia. It can be reached by dietary treatment; however, if it fails, maternal glycemic monitoring or combined fetal-maternal monitoring, or even insulin (if required) can help reach it. Multiple daily insulin regimens are becoming more widely accepted for the treatment of GDM. Insulin analogues, however, need some more evidence to support their usefulness and safety during pregnancy. The screening for GDM, the reclassification, regular care, and follow-up of these women after pregnancy are of the utmost importance to delay or prevent not only type 2 diabetes but cardiovascular complications as well.