The purpose of this study was to determine the prevalence of insulin resistance syndrome (IRS) and the risk factors for developing IRS among women with a history of gestational diabetes mellitus (GDM), compared with controls over 11 postdelivery years. Assessments of 106 women with a prior history of GDM and 101 controls were done on six occasions from 4-11 yr after delivery. Tests included glucose, insulin, lipids, blood pressure, and body measurements. The risk of IRS was analyzed by Cox regression. The results were that 27.2% of GDM and 8.2% of controls developed IRS by 11 yr after delivery. The hazard of developing IRS was 5.6 times (95% confidence interval = 2.6-12.3) among women with prepregnant obesity (body mass index >27.3 kg/m(2)), compared with women without prepregnant obesity and 4.4 times (95% confidence interval = 1.7-11.1) in women with a history of GDM, compared with controls. At 11 yr after delivery, the cumulative hazard for developing IRS in the next 2 yr was 26 times higher among GDM with prepregnant obesity, compared with controls without prepregnant obesity. We concluded that obesity and GDM in a prior pregnancy are significant risk factors for developing IRS over time. Early detection of markers of IRS is vital for possible prevention of type 2 diabetes and cardiovascular adverse events in women.