OBJECTIVE:--To determine whether 1-h oral glucose challenge test (OGCT) or 3-h oral glucose tolerance test (OGTT) results below gestational diabetes mellitus (GDM) criteria are associated with developing diabetes. RESEARCH DESIGN AND METHODS--A retrospective cohort study was performed among women without GDM who had a pregnancy OGCT (n = 24,780) or OGTT (n = 6,222). Subsequent diabetes was ascertained by ICD-9 codes or pharmacy or laboratory data over a median follow-up of 8.8 years. RESULTS:--Diabetes risk increased across OGCT quartiles: adjusted hazard ratio (HR) 1.67 (95% CI 1.07-2.61) for 5.4-6.2 mmol/l, 2.13 (1.39-3.25) for 6.3-7.3 mmol/l, and 3.60 (2.41-5.39) for >=7.4 mmol/l compared with <=5.3 mmol/l. Women with one abnormal OGTT result had a higher risk compared with those with normal values (HR 2.08 95% CI 1.35-3.20). CONCLUSIONS:--Women with modestly elevated glucose levels below the threshold for GDM had a higher risk for diabetes.