As a result of the rising prevalence of childhood obesity, there is an increasing interest in the type 2 diabetes mellitus precursor insulin resistance (IR). The aim of this study is to review definitions (methods and cutoff values) to define IR in children and to apply these definitions to a previously described obese pediatric population. A systematic literature review on prevalence and/or incidence rates in children was performed. The extracted definitions were applied to an obese pediatric population. In the 103 identified articles, 146 IR definitions were reported based on 14 different methods. Fasted definitions were used 137 times, whereas oral/intravenous glucose tolerance test-derived methods were used nine times. The homeostasis model for the assessment of insulin resistance (HOMA-IR) and fasted plasma insulin (FPI) were the most frequently used fasted methods (83 and 37 times, respectively). A wide range in cutoff values to define IR was observed, resulting in prevalence rates in the predefined obese pediatric population between 5.5% (FPI>30 mU/L) and 72.3% (insulin sensitivity indexMatsuda≤7.2). To compare IR incidence and prevalence rates in pediatric populations, a uniform definition of IR should be defined.