Abstract    INTRODUCTION: The study was conducted to define the determinants of suboptimal blood pressure (BP) control among hypertensive patients under treatment and explore a predictive model for detecting the patients at risk for increased BP.    METHODS: We enrolled 97 patients (40 males, 57 females) under treatment for hypertension between June 2006 and May 2007 in Shafa hospital, Kerman, Iran. BP was measured at clinic twice within 5-minute intervals. After setting up ambulatory blood pressure monitoring (ABPM), BP was measured at 30-minute intervals during the day and 60-minute intervals during the night. The frequency of increased BP (more than 140/90 mmHg) was included in a regression model as dependent variable and all the others such as age, sex, body mass index (BMI), drugs and baseline clinical measurements as the predictors.    RESULTS: Increased BP was detected in 44% (95% CI: 38.79%-49.65%) of all measurements during 24-hour monitoring. The frequency of increased BP had a significant relationship with BMI (b=0.35, P=0.001). Clinic's pulse pressure was a significant predicting factor for BP increase (P=0.02).    CONCLUSION: BMI and pulse pressure are the best predictors for being hypertensive during lifetime. Ineffective treatment of hypertension is frequent among the hypertensive patients.      Keywords: Blood pressure control, Pulse pressure, Ambulatory blood pressure monitoring (ABPM), BMI.