This study compares relationships between each of morning home blood pressure (BP), evening home BP and office BP with electrocardiographic (ECG) abnormalities among treated hypertensive Japanese patients. We defined ECG left ventricular hypertrophy (LVH) as Sokolow-Lyon voltage and/or Cornell voltage duration product. Abnormal T waves and ST segment depression were categorized based on the Minnesota code. Office BP was calculated as the mean of four readings taken during two visits. Morning and evening home BP were calculated as the mean of five readings measured once each morning and evening for 5 days, respectively. Multivariate analysis showed that ECG-LVH in 747 hypertensives (mean age: 72 years; women: 63%) was more closely associated with morning home BP than with either office or evening home BP. Even the first reading of morning home BP on day 1 was significantly associated with ECG-LVH independently of office BP. The association between home BP and ECG-LVH increased with the cumulative number of home BP measurements. The results for abnormal T waves were similar. Home and office BP did not significantly differ between patients with and without ST segment depression. Morning home BP was more closely associated with ECG-LVH and abnormal T waves than either office or evening home BP among treated hypertensive Japanese patients.