The aim of this study was to evaluate the glycemic measures from an oral glucose tolerance test (OGTT) during pregnancy as predictors of incident type 2 diabetes mellitus (T2DM). Patients diagnosed with gestational diabetes mellitus (GDM) were divided into two groups according to the results of OGTT: one abnormal value?=?GDM1 (n?=?338) and two abnormal values?=?GDM2 (n?=?151), while women with normal glucose tolerance served as controls (n?=?385). Glucose tolerance was re-evaluated with an OGTT in a follow-up study (average follow-up time 7.3?±?5.1 years). The incidence of T2DM after 10 years follow-up increased progressively by the degree of the glycemic abnormality during pregnancy: 0.8% in controls, 3.8% in GDM1 (adjusted HR 17.6, 95% CI 1.9-162.3) and 25.0% in GDM2 (adjusted HR 72.9, 95% CI 9.6-553.7), respectively (p?=?