Women with a history of gestational diabetes mellitus (GDM) are at increased risk of future diabetes, predominantly type 2 diabetes, as are their children. The extent of this risk depends both on the diagnostic criteria used to identify GDM and on maternal risk factors, some of which are potentially modifiable whereas others are not. The unmodifiable risk factors are ethnicity, pre-pregnancy weight, age, parity, family history of diabetes, and degree of hyperglycemia in pregnancy and immediately postpartum. The modifiable risk factors are persistent obesity, future weight gain, and subsequent pregnancies. Additional modifiable risk factors in these women are likely to be levels of physical activity, dietary fat, and avoidance of other lifestyle factors that adversely influence insulin resistance, such as smoking and certain drugs. Diabetic prevention strategies need to address the potentially modifiable risk factors using the unmodifiable risk factors to identify women most at risk.