Introduction: The obesity epidemic has become one of the most important public health issues of modern times. Impaired insulin sensitivity seems to be the cornerstone of multiple obesity related comorbidities. However, there is no accepted definition of impaired insulin sensitivity. Objective: We hypothesize that assessment of insulin resistance differs between centers. Methods: The ESPE Obesity Working Group (ESPE ObWG) Scientific Committee developed a questionnaire with a focus on the routine practices of assessment of hyperinsulinemia and insulin resistance, which was distributed through Google Docs platform to the clinicians and researchers from the current ESPE ObWG database (n = 73). Sixty-one complete responses (84% response rate) from clinicians and researchers were analyzed: 32 from European Union (EU) centers (representatives of 14 countries) and 29 from Non-EU centers (representatives from 10 countries). Standard statistics were used for the data analysis. Results: The majority of respondents considered insulin resistance (IR) as a clinical tool (85.2%) rather than a research instrument. For the purpose of IR assessment EU specialists prefer analysis of the oral glucose tolerance test (OGTT) results, whereas non-EU ones mainly use Homeostatic Model Assessment of Insulin Resistance (HOMA-IR; p = 0.032). There was no exact cutoff for the HOMA-IR in either EU or non-EU centers. A variety of OGTT time points and substances measured per local protocol were reported. Clinicians normally analyzed blood glucose (88.52% of centers) and insulin (67.21%, mainly in EU centers, p = 0.0051). Furthermore, most participants (70.5%) considered OGTT insulin levels as a more sensitive parameter of IR than glucose. Meanwhile, approximately two-thirds (63.9%) of the centers did not use any cutoffs for the insulin response to the glucose load. Conclusions: Since there is no standard for the IR evaluation and uniform accepted indication of performing, an OGTT the assessment of insulin sensitivity varies between EU and non-EU centers. A widely accepted standardized protocol is needed to allow comparison between centers.