This is a lifestyle intervention project tailored to pregnant and postpartum women with gestational diabetes (GDM) and designed to reduce risk factors for type 2 diabetes. The intervention will start during pregnancy soon after GDM diagnosis and will continue postpartum. It will be delivered by individual telephone counseling contacts and brief in-person counseling sessions. Patients will be randomly assigned to a lifestyle intervention or usual medical care. Among GDM patients we propose to implement and evaluate an intervention of diet and physical activity tailored to be practical in health plan settings and for postpartum mothers, with the primary goals of: a) reaching pre-pregnancy weight if women had normal pre-pregnancy weight; or b) reaching a 5% reduction from pre-pregnancy weight if overweight or obese prior to pregnancy.