Gestational diabetes mellitus (GDM) is a common pregnancy complication with increased maternal and perinatal morbidity. However, significant long-term morbidity also exists for the mother and offspring. Women with previous GDM have a very high risk of developing overt diabetes, primarily type 2 diabetes, later in life. Moreover, the risk of the metabolic syndrome is increased 3-fold in these women. Their offspring have an 8-fold risk of diabetes/prediabetes at 19-27 years of age. Thus, GDM is part of a vicious circle which increases the development of diabetes in the coming generations.