Cross-sectional studies have shown that home blood pressure (BP) correlates with hypertensive target organ damage better than clinic BP. However, there have been few longitudinal studies regarding the predictive value of home BP on the changes in organ damage in treated hypertensive patients. Clinic and home BP over a 12-month period, antihypertensive medication use, echocardiographic and electrocardiographic results, and serum creatinine and urinary protein levels were examined in 209 treated hypertensive patients in 1993. These patients were prospectively followed for 5 years. The patients were divided into 4 subgroups according to hypertension control as follows: good control (<140/90 mmHg for clinic BP, <135/85 mmHg for home BP), improved, worsened, and poor control. The average clinic BP was 147.0+/-14.9/87.0+/-7.6 mmHg (mean+/-SD) in 1993 and 146.0+/-13.7/84.1+/-7.5 mmHg in 1998. The average home BP was 136.8+/-10.4/84.3+/-7.6 mmHg in 1993 and 136.1+/-9.7/81.2+/-7.7 mmHg in 1998. The left ventricular mass index (LVMI) positively correlated with both home systolic BP and clinic systolic BP in 1998 but not in 1993. The correlation tended to be closer for home BP than for clinic BP. LVMI did not change in patients with good or improved home systolic BP, while it increased in those with poor or worsened home systolic BP. The relationship between changes in LVMI and clinic BP was not significant. In conclusion, Home BP was more effective than clinic BP as a predictor of changes in left ventricular hypertrophy in treated hypertensive patients. Home BP should be controlled to below 135/85 mmHg to prevent cardiac hypertrophy.