Atherosclerosis is increasingly recognized as an inflammatory vascular disease, and high blood pressure (BP) has been suggested to exert a proinflammatory action. Whether plasma viscosity (PV), a major determinant of blood flow in microcirculation and a marker of systemic inflammation and cardiovascular risk, is increased in elderly subjects with isolated systolic hypertension is not known. In addition, the correlation of BP and its pulsatile component (ie, pulse pressure [PP]), with PV levels independent of the confounding effect of other cardiovascular risk factors has not been investigated. To this aim, we measured PV in 108 elderly men with never treated, uncomplicated isolated systolic hypertension, and in 60 healthy matched normotensive control subjects. The PV values were higher in hypertensive subjects than in controls (1.39+/-0.11 v 1.34+/-0.09 cP, P<.01). The PV showed a significant direct relation with both systolic BP (r=0.32) and PP (r=0.37, both P<.01), but not with diastolic BP (r=-0.03, P=.68). The PV was also directly associated with serum low-density lipoprotein cholesterol and triglycerides. In a multivariate analysis, PP was a significant predictor of PV levels when a consistent number of cardiovascular risk factors were simultaneously controlled for. In conclusion, PV is elevated in elderly subjects with isolated systolic hypertension. Systolic BP and PP appear to be major determinants of PV levels in these patients, independent of the potential proinflammatory action of traditional cardiovascular risk factors.