Objective: To compare the 4th International Workshop-Conference on Gestational Diabetes Mellitus (GDM) 100-g OGTT (NEW) criteria to the current ACOG criteria. Methods: An analysis of a comprehensive perinatal database (1991–1998) identified women with singletons who underwent a 100-g OGTT after an abnormal 50-g GCT performed at 24 weeks or more. Women were classified into three groups for comparison: those who met the ACOG criteria and received diet or insulin therapy or both; those who did not meet ACOG criteria, but did meet the NEW criteria; and those who met neither criteria (non-GDM). Results: Of 3,253 women, 478 women met ACOG criteria, 319 women would have been reclassified as GDM by the NEW criteria, and 2,456 women met neither criteria. The selected characteristics and outcomes (%) for the three groups are as follows: After controlling for confounders (including maternal weight, age, race, parity, and smoking status), the adjusted odds ratios and 95% CI, compared with non-GDM women are as follows: Conclusions: At our institution, utilization of the NEW criteria would increase the diagnosis of GDM by 40% and identify gravidas with similar risks of cesarean delivery and macrosomia as those with GDM diagnosed by ACOG criteria. Whether or not standard GDM therapy in women with the disease diagnosed by the NEW criteria can reduce the incidence of cesarean delivery and macrosomia to rates comparable with non-GDM women remains to be verified by well-designed randomized controlled studies.