Accurate measurement of blood pressure (BP) and evaluation of global cardiovascular risk is crucial for diagnosis and treatment of hypertensive patients. When hypertension and diabetes mellitus are associated, the risk for cardiovascular events is bigger than the sum of the components. Beyond systolic and diastolic BP values as targets for antihypertensive treatment, recent guidelines recognize BP variability as an independent predictor for future cardiovascular events. 24 hours ambulatory BP monitoring (ABPM) and home BP monitoring (HBPM) are two methods used in patient day to day life conditions for BP measurements. Increased variability of systolic and/or diastolic BP within one day (“short-term BP variability”) and also over longer periods (“long-term BP variability”) showed by ABPM and/or HBPM is associated with target-organ damage and cardiovascular events. This review is focused on the prognostic importance of BP variability in hypertensive patients with diabetes mellitus.