Although it is recognized that the cause of hypertension can be various, once blood pressure has become established structural changes emerge in the systemic vasculature. In medium- and large-sized vessels, as in the left ventricle, there is clear histological evidence of hypertrophy of the medial smooth muscle layers but, downstream in small arteries, which modulate vascular resistance, other changes occur. In essential hypertension, the smooth muscle cells of small vessels are restructured around a smaller lumen, but there is no evidence of hypertrophy or hyperplasia of the vascular wall. In secondary forms of hypertension, which tend to be representative of severer forms of the disease, hypertrophic remodelling is observed. Similarly, in non-insulin-dependent diabetes mellitus, irrespective of whether blood pressure accompanies this disorder or not, hypertrophy is also seen. The presence of architectural alterations in the vascular wall of small arteries may have a strong prognostic significance in patients, and this may be over and above all other known cardiovascular risk factors. Although it is yet to be established whether regression of such changes should be a goal of effective antihypertensive therapy, there is a body of evidence emerging indicating that different classes of antihypertensive drug have a varied effect on reversing vascular structure both in humans and animal models of genetic and experimental hypertension. However, at present, there are no data available concerning the prognostic impact of regressing vascular structural alterations in hypertension, and this must be an urgent research priority.