Microalbuminuria is usually defined as a urinary albumin excretion of 30-300 mg/24 h (i.e. 20-200 micrograms/min) measured, in view of the short-term variation of 15-30%, in at least 2 out of 3 urine samples. An alternative definition is: an albumin-creatinine ratio of 2-20 mg/mmol creatinine. Microalbuminuria is an indicator of an enhanced risk of chronic kidney failure and cardiovascular disease in diabetic patients and of cardiovascular disease in the elderly general population. It is not known whether these relationships exist in essential hypertension as well. In essential hypertension there is, however, a relationship between microalbuminuria and endothelial dysfunction, impaired regulation of renal haemodynamics and an increased risk of left ventricular hypertrophy and hypertensive retinopathy. By screening for microalbuminuria a group of patients can be distinguished who have a relatively high risk for the presence of complications of hypertension. It is not certain, however, that more intensive treatment of such patients (e.g. with ACE inhibitors) is useful. Consequently, for the time being, screening of patients with essential hypertension for microalbuminuria is of little practical importance.