Introduction:Microvascular diabetic complications are the most common causes of morbidity and mortality in patients with type 1 DM. The main etiology for mortality and a great percent of morbidity in patients with diabetes mellitus is atherosclerosis. A hypothesis for the initial lesion of atherosclerosis is endothelial dysfunction Aim:This study aims to evaluate the incidence of endothelial dysfunction in type 1 DM in relation to glycaemic control , duration of disease and other factors using Doppler ultrasound. Methods:A prospective case control study was conducted on 50 type 1 DM cases and 50 matched controls over a period of one year from January 2018 to December 2018 using colour doppler ultrasonography of brachial artery. Results:It was observed that among the 50 type 1 DM , endothelial dysfunction was (FMD<10%) present among 19 (38%) cases and 1 (2%) controls. Macroalbuminuria as measured by urine ACR was present in 3 cases (6%) of type1 DM while none of the controls had macroalbuminuria. Microalbuminuria was present in 13 cases (26%) and 4 controls (8%). Diabetic Retinopathy was noted in 7 cases of Type 1 DM (14%) and all of them had endothelial dysfunction. Conclusion:Endothelial dysfunction was seen in all duration of diabetes (<5, 5-10, >10 years) and prevalence increased with duration of diabetes. Identification of endothelial dysfunction early in the course of Type 1 DM, it may be possible to delay the development of microvascular and macrovascular complications, ultimately reducing the morbidity of the disease.