To identify subjects who would most likely benefit from oral glucose tolerance test (OGTT) for diagnosis of diabetes mellitus (DM), namely isolated postchallenge hyperglycemia (IPH) (i.e. FPG<126mg/dl and 2h-PG>or=200mg/dl), we evaluated data and results of OGTT of 9745 participants of Tehran Lipid and Glucose Study (TLGS), aged >20 years and without previously diagnosed DM. The overall prevalence of IPH was 3.1% (95% CI: 2.8-3.4%, n=302). In the multivariate logistic regression analysis, the odds ratios (OR) for IPH were statistically significant for FPG>or=100mg/dl (OR 9.5; 95% CI: 7.1-12.5), age >or=40 years (OR 2.6; 95% CI: 1.8-3.7), triglycerides >or=200mg/dl (OR 2.1; 95% CI: 1.6-2.7), hypertension (OR 2.0; 95% CI: 1.5-2.6) and abnormal waist circumference (OR 1.9; 95% CI: 1.3-2.8). In subjects with FPG<126mg/dl, findings that best distinguished between IPH and non-diabetic subjects were FPG>or=100mg/dl [positive likelihood ratio (LR(+))=5.2], FPG>or=100mg/dl together with triglycerides >or=200mg/dl [LR(+)=9.7] and a combination of all the five factors [LR(+)=12.9]. This analysis showed that in Iranian urban subjects with FPG<126mg/dl, factors such as FPG>or=100mg/dl, older age, hypertriglyceridemia, hypertension and abnormal waist circumference were the best predictors of presence of IPH; OGTT would hence be recommended for opportunistic screening of IPH in subjects with above mentioned characteristics.