Many patients believe that their diabetes has been caused by stress or an adverse life event. Whereas there is strong evidence that psychological stress is related to a deterioration in glycaemic control in established diabetes, there is much less evidence that psychological stress can cause diabetes in humans de novo. It seems more likely that psychological stress produces a deterioration in glycaemia in the non-symptomatic patient which in turn makes diabetic symptoms and the diagnosis evident. The pathogenic mechanisms which have been suggested to relate psychological stress to diabetes are described and reviewed.