In developed countries, obesity prevalence has strongly increased in the last decades. This has also been observed in children and adolescents. Until recently, type 2 diabetes mellitus was considered very rare among children and adolescents; however, in the last decades, some cases have been observed mainly in obese adolescents of some minority populations. The aim of our study was to assess the prevalence of type 2 diabetes, impaired glucose tolerance (IGT) and insulin resistance, and the metabolic features, in obese children and adolescents. We have studied 95 obese children and adolescents, 53 males and 42 females, aged 4-16 years. The prevalence of IGT in obese children and adolescents studied was 7.4%; there was not any child with type 2 diabetes. Fasting glucose and insulin serum concentrations did not show significant differences between obese children with or without IGT; however, 120 minutes after an oral glucose tolerance test, glucose and insulin serum concentrations showed statistically significant differences between both groups. Insulin resistance is defined as a HOMA index higher than 4. The prevalence of insulin resistance in obese children studied was 35.8%. Trygliceride serum concentrations were higher and HDL-C serum concentrations were lower in obese children with IGT than in those without IGT, but the differences were not statistically significant. IGT and insulin resistance are frequent in obese children and adolescents; early treatment in obese children and adolescents with IGT constitutes a strategy of reversing progression to beta-cell failure and in preventing type 2 diabetes.