Background: Diabetes mellitus is a general disorder that changes the main metabolic processes that distressing the functions of systems in the body. Type 1 diabetes is the generally common metabolic disorder of adulthood. Around one in each 400–600 juveniles and adults has type 1 diabetes. Its incidence has risen over new years. Objective: To evaluate corneal endothelial alterations in type I diabetic patients with or without diabetic retinopathy. Patients and Methods: A prospective comparative study of 60 subjects divided into two equal groups: Group A: with type I DM with or without diabetic retinopathy and Group B: normal persons matched with age and sex. All patients were subjected to  full history and ophthalmic examination including  Uncorrected / best corrected visual acuity (UCVA/BCVA) expressed in LogMar scoring, refraction using automated refractometer (Topcon KR-800 Auto refractometer), intraocular pressure (IOP) measurement by Goldman Applanation tonometer, Slit lamp biomicroscopy to assess corneal clarity, depth of anterior chamber, state of pupil dilatation, lens morphology, state of diabetic retinopathy in dilated pupil fundus examination and non-contact specular microscope (Topcon sp-1p, Topcon Medical Inc., Japan) to assess the corneal endothelium and patients were compared to normal persons as regard: endothelial cell density (ECD), coefficient of variation in cell size (CV), changes in percentage of hexagonal cells (HEX) and central corneal thickness (CCT). The study was done at Department of ophthalmology, Sayed Galal University Hospital, Cairo, Egypt and it was carried out from May 1ˢͭ, 2019 to April 30ͭ ͪ   2020. Results: Among patient group, twenty one (70%) patients were females while nine (30%) patients were males. Ten persons (20 eyes) in study group were diabetics with diabetic retinopathy. There was a significant decrease in ECD, and a significant increase in CCT, also there was a significant change in CV, and HEX an increase in CV (polymegathism) and decrease in hexagonality (pleomorphism) in type I diabetic patients. Diabetic retinopathy and duration of diabetes were factors that affect central corneal thickness. Conclusion: Cornea of a diabetic patient has lower ECD compared to normal and thicker cornea than non-diabetics also with higher coefficient of variation and lower hexagonality.