Introduction: Approximately 40% of women with gestational diabetes mellitus (GDM) diagnosed using International Association of the Diabetes and Pregnancy Study Group (IADPSG) criteria require insulin therapy.Objective: We assessed whether the outcomes for women with GDM treated with insulin are comparable to women with normal glucose tolerance (NGT). Materials and Methods: This retrospective cohort study included 752 women with insulin-treated GDM and 2496 women with NGT during pregnancy. Maternal and fetal outcomes were examined.Results: Infants of women with insulin-treated GDM had rates of macrosomia [adjusted odds ratio (aOR), 1.19; 95% confidence interval (CI), 0.87 to 1.63; P = 0.26], large for gestational age (LGA) (aOR, 1.07; 95% CI, 0.77 to 1.47; P = 0.67), and small for gestational age (SGA) (aOR, 0.70; 95% CI, 0.38 to 1.38; P = 0.26) similar to women with NGT. They were more likely to be hypoglycemic at birth (aOR, 6.85; 95% CI, 2.31 to 20.28; P<0.01) and to require neonatal intensive care unit care (NICU) (aOR, 12.09; 95% CI, 8.72 to 16.76; P, 0.01), predominantly for nonmedical reasons. Maternal rates of hypertensive disorders (preeclampsia: aOR, 0.64; 95% CI, 0.34 to 1.12; P = 0.17; pregnancy-induced hypertension: aOR, 1.11; 95% CI, 0.74 to 1.66; P = 0.60) and hemorrhage (ante partum hemorrhage: aOR, 0.56; 95% CI, 0.19 to 1.58; P = 0.27; postpartum hemorrhage: aOR, 1.17; 95% CI, 0.68 to 2.03; P = 0.55) were similar between groups, but the risk of polyhydramnios was increased in the GDM cohort (aOR, 7.75; 95% CI, 3.96 to 15.16; P, 0.01).Conclusions: Insulin treatment of IADPSG-diagnosedGDMresults in rates of macrosomia, LGA, SGA, and maternal hypertensive disorders similar to those of women with NGT. Although NICU admissions are greater in the GDM cohort, they are primarily for nonmedical reasons. Neonatal hypoglycemia and polyhydramnios remain greater among women with insulin-treated GDM.