Diabetic complications are common, costly and have a major impact on length and quality of life. There is good evidence that they can be delayed or even prevented in type 1 and type 2 diabetes by achievement of normoglycaemia, control of other risk factors, regular review and early treatment. This article discusses the type of damage that can occur in both type 1 and type 2 diabetes, which patients are particularly vulnerable and why, the costs of diabetic complications, how they can be prevented, the nursing implications of caring for patients who already have damage and helping to prevent it in others.