Patients with type 1 and 2 diabetes and nephropathy frequently have a blunted fall in nighttime arterial blood pressure. This abnormality is already seen in subjects with type 1 diabetes who are in the microalbuminuric phase of the disease, and we have also shown that an increase in nighttime systolic blood pressure precedes the development of microalbuminuria. These studies suggest that nocturnal hypertension may be an important early predictor of diabetic nephropathy. Various drugs have different effects on nocturnal blood pressure, and chronotherapy may be key in determining clinical outcomes. There is a compelling need for studies showing that treating nocturnal hypertension in diabetes can prevent renal disease progression.