The Diabetes Control and Complications Trial (DCCT)/Epidemiology of Diabetes Interventions and Complications (EDIC) study has allowed an examination of the long-term effects of type 1 diabetes and intensity of treatment on cognitive function. The association observed between chronic hyperglycaemia and mild cognitive dysfunction, affecting motor speed and psychomotor efficiency, has been re-evaluated by Jacobson et al. (Diabetologia doi: 10.1007/s00125-010-1883-9) to determine the possible contribution of macrovascular risk factors, subclinical macrovascular disease and microvascular complications (retinopathy and nephropathy). This has revealed associations between mild impairment of psychomotor efficiency and hypertension, glycaemic control and the presence of retinopathy and nephropathy, while smoking history was associated with modest abnormalities in several cognitive domains. Neither macrovascular risk factors nor a history of severe hypoglycaemia was associated with the cognitive decrements; cerebral microangiopathy has been proposed as a possible underlying cause. Although the degree of cognitive impairment was mild and limited to a few domains, these decrements may influence the performance of everyday activities, such as driving.