Patients with type 1 diabetes (T1D) have greater rate and faster progression of cognitive decline than their age peers. Its mechanism was directed to microvascular pathway [1]. T1D induces regional microvascular changes in cortical and subcortical brain structures that are associated with impairment of neurocognitive functions. Microvascular complications, such as diabetic retinopathy, distal symmetric polyneuropathy, and renal complications are each independently associated with cognitive declines in T1D [1]. Recent evidence suggested that the presence of macrovascular complications and other metabolic factors also independently contribute to cognitive decline [2]. Insulin resistance (IR) is proposed as the link of type 2 diabetes to cognitive decline. Although IR has also been quantifed in T1D, it remains unclear if IR is associated with cognitive decline in T1D. By analyzing the data set from Diabetes Control and Complications Trial/Epidemiology of Diabetes Interventions and Complications study (DCCT/EDIC) study, we test the hypothesis that the cognitive decline occurring in T1D is associated with IR.