This review article outlines the evidence that 24 h blood pressure (BP) measurements are particularly important predictors of adverse cardiovascular outcome. In turn, there is supportive evidence from a range of studies that 24 h BP control should be an integral part of the antihypertensive drug treatment strategy. Furthermore, since not all once daily antihypertensive agents can provide such 24 h control, there is a requirement for careful drug (and/or dosage) selection. Although the clinic (office) BP continues to be the standard measurement by which hypertension is diagnosed and treatment monitored, there is now clear evidence of the superiority of 24 h BP assessments. Although there are not yet prospective, outcome clinical trails which have relied upon 24 h BP values there is clear evidence that 24 h BP values correlate much more closely than conventional clinic BP values with measurements such as left ventricular hypertrophy, cerebral vascular damage (lacunar infarcts), renal damage (microalbuminuria) and vascular damage (carotid artery intima media thickness). In turn, there is evidence that during drug treatment, when achieved clinic blood pressures appear to be comparable, there is improved outcome in those patients whose 24 h BP values are significantly lower. Not all antihypertensive drugs are equivalent, however, in their abilities to reduce 24 h BP and the clinician needs to be aware of possible shortcomings when considering the choice of drug. In this respect, intrinsically long-acting agents are best equipped to provide sustained and consistent BP control throughout 24 h.