Left ventricular hypertrophy (LVH) and cuff blood pressure (BP) level are not as closely related as one might suppose. A better correlation was reported between LVH and continuous monitoring of BP. To analyze this relationship we performed continuous intra-arterial ambulatory monitoring (Oxford technique) in 10 patients with essential hypertension (EH) having LVH, and in 10 age-matched EH patients with normal left ventricles (NLV). Average cuff BP did not differ significantly between the two groups. The intra-arterial BP monitoring showed a significantly higher systolic BP in EH patients with LVH for the mean of the 24 hours (p less than .05) and in the 6 PM-6 AM (night) period (p less than .01); whereas the difference was not significant for the mean systolic BP of the 6 AM-6 PM (day) period and for the mean 24-hour diastolic BP. The heart rate was similar between the two groups; however, the variability of BP was not different. The night systolic BP correlated with the thickness of interventricular septum plus left ventricular posterior wall (LVPW) (r = 0.66; p less than .05). These results may have therapeutic implications, although they require confirmations in a larger series of patients.