Insulin resistance (IR) is a fundamental disorder of type 2 Diabetes Mellitus (DM), but it is also involved in the etiopathogenesis of type 1 DM, with important implications in the onset and progression of micro- and macrovascular complications in type 1 DM. Overweight plays the main role in the increased incidence of both types of DM, exacerbating IR. The epidemic increase of overweight and obesity makes it difficult to diagnose the exact phenotype of DM, as IR and autoimmunity often coexist. Many studies showed an increase in incidence of micro- and macrovascular complications in patients with type 1 DM with IR, compared to patients with type 1 DM without IR. The gold standard of IR evaluation is represented by the method of euglycemic-hyperinsulinemic clamp, applied on a reduced scale in research. Thus, it is necessary to identify early IR markers (clinical or biological markers), less laboured ones, that could be used on a large scale in current medical practice, for the IR determination in type 1 DM. Clinicians and health experts should prevent/ reduce the epidemic of overweight and obesity in young people, thus decreasing IR, and implicitly the chronic complications of DM.