Nineteen patients with idiopathic normal pressure hydrocephalus (NPH) were treated with intraventricular shunts. Ten of the 14 who improved and 14 of the total group had systemic hypertension. The prevalence of hypertension in both the improved and whole NPH groups was significantly greater than in a control group with dementia (N = 122) and the published prevalence of hypertension in the US population for this age group. Four possible mechanisms for this association are discussed.