In this cross-sectional study, we evaluated results of oral glucose tolerance test (OGTT) from4742 women and 3470 men, participated in the Tehran Lipid and Glucose Study, aged 20years and without diabetes, to determine the diagnostic value of subjects’ clinical traits withisolated impaired glucose tolerance (isolated-IGT) defined as fasting plasma glucose (FPG)<5.6 mmol/L and 2-h plasma glucose between 7.8 and 11.1 mmol/L. The overall prevalenceof IGT was 13.6% (n = 1120); of these subjects, 59.6% (n = 668) had isolated-IGT. The adjustedodds ratios for having isolated-IGT among 7012 subjects with FPG <5.6 mmol/L weresignificant for age 40 years (2.5), hypertension (1.9), abnormal waist circumference (1.9),obesity (1.5), and family history of diabetes (1.3). Adding the lipid profiles to the clinicalmodel increased the area under the ROC curve only slightly (73.2% vs. 72.1%, respectively;P = 0.002). In summary, this study showed that in adults with FPG <5.6 mmol/L, older age,family history of diabetes, abnormal waist circumference and obesity, and hypertensionwere significantly associated with a higher likelihood of isolated-IGT; OGTT could hence berecommended in subjects who have most of these characteristics to find Isolated-IGT,especially if the findings are supported by appropriately designed clinical trials.