Chronic elevation in bp (systolic ≥140 mmHg or diastolic ≥90 mmHg); etiology unknown in 80-95% of pts (“essential hypertension”). Always consider a secondary correctable form of hypertension, especially in pts under age 30 or those who become hypertensive after 55. Isolated systolic hypertension (systolic ≥140, diastolic <90) most common in elderly pts, due to reduced vascular compliance.