Morning blood pressure (BP) level may play an important role in the pathogenesis of cardiovascular events; however, morning BP detected by home BP monitoring may remain uncontrolled in medicated hypertensive patients even when clinic BP is well controlled (masked morning hypertension: MMHT). We studied the determinants of MMHT in stably medicated hypertensive outpatients. In the Jichi Morning Hypertension Research (J-MORE) study, 969 consecutive hypertensive outpatients were recruited by 43 doctors in 32 different institutes. They had been under stable antihypertensive medication status at least for 3 months. Clinic BP was measured on 2 different days and self-measured BP monitoring was conducted twice consecutively in the morning and evening for 3 days.