This paper presents an analysis of the literature regarding the effect of control of diabetes on retinopathy. In diabetics with age of onset before forty years of age and with a duration greater than fifteen years, there is a significantly higher in?cidence of retinopathy in those judged to have been under poor control than in those with better control. Those patients with poor control had a significantly higher incidence of the more severe forms of diabetic retinopathy. While this association does not necessarily imply a cause and effect relationship, it is not compatible with a point of view which accepts poor control as of little consequence in diabetes.