A reduced fall in nocturnal blood pressure (BP) (i.e. non-dipping) has been related to an increase in target organ damage and cardiovascular (CV) events. Numerous studies have shown that non-dipping is highly prevalent in patients with type 1 and 2 diabetes mellitus. In this paper we reviewed recent literature and our personal data on the prevalence and clinical correlates of abnormal diurnal BP rhythm in diabetic patients; in particular we examined the association of this condition with renal, cardiac, and vascular pre-clinical organ damage as well as CV prognosis. A consistent body of evidence based on cross-sectional and longitudinal studies indicates that the lack of the physiologic nocturnal fall in BP may be considered a true clinical trait, a reliable marker of preclinical CV and renal disease and an independent predictor of future CV events. Thus, in the diabetic setting ambulatory BP monitoring (ABPM) should be regarded as a pivotal tool for improving CV risk stratification and therapeutic interventions.