Diabetic retinopathy (DR) is one of the most serious complications of diabetes mellitus, which is also the main cause of adult blindness. The complex pathogenesis involves a variety of biochemical abnormalities. Some of the major pathways implicated are augmentation of the polyol pathway, protein kinase C activation, increased oxidative stress, advanced glycation end product formation, increased expression of growth factor and adhesion molecules. This article reviewed DR and its pathogenesis.