Prediabetes is characterized by isolated impaired fasting glucose (IFG), isolated impaired glucose tolerance (IGT), and combined IFG/IGT. This study aimed to establish the prevalence of prediabetes and examine possible contributory factors in a cohort of obese adolescents.In this prospective study, we recruited 85 obese patients from the Obesity Clinic at the University Children's Hospital and 17 normal weight controls. All patients were of Caucasian origin, 60 males/42 females, aged 7.4-18.3 years, with at least Tanner 2 stage of puberty.Depending on criteria we used, insulin resistance was confirmed in 62-100% of obese patients, predominantly in the group with BMI SDS > 3. oGTT revealed isolated impaired fasting glucose (IFG) in 13.9%, impaired glucose tolerance (IGT) in 20.8% and combined IFG and IGT only in 2.8% of the obese patients. Patients in the prediabetes group were older (14±2.4 vs 12.8±2.5 p=0.04) and had higher glucose levels (p<0.001) during the whole oGTT compared to normal glucose tolerance (NGT) group. There was no difference between groups in respect to family history, BMI, lipids and fasting insulin. Insulinogenic index, WBISI and HOMA%B were significantly lower in the prediabetes group compared to the NGT group (p=0.07, 0.01 and 0.04 respectively). HbA1c level was measured in 58% of patients and was significantly higher in the prediabetes group (5.4±0.3 vs 5.7±0.4, p=0.002).Prediabetes occurrence was fairly high in our obese adolescents. Further studies should establish what would be the most appropriate screening test to diagnose these patients at risk for type 2 diabetes and initiate treatment without delay.