Previous studies have shown that in the population, only a minority of treated hypertensive patients achieve blood pressure (BP) control. Whether and to what extent this inadequate control has reflection on hypertension-related organ damage has never been systematically examined. In 2051 subjects belonging to the PAMELA (Pressioni Arteriose Monitorate E Loro Associazioni) Study population, we measured office, home, and 24-hour ambulatory BP values, together with echocardiographic left ventricular mass and wall thickness. Based on the fraction on antihypertensive treatment and on measurements of increased or normal office, home, or 24-hour ambulatory BP values, subjects were classified as normotensives, untreated hypertensives, treated hypertensives with inadequate BP control, and treated hypertensives with effective BP control. Compared with values in the normotensive group, left ventricular mass index, left ventricular wall thickness, and prevalence of left ventricular hypertrophy were markedly increased not only in untreated hypertensive patients but also in treated hypertensives with inadequate BP control. Echocardiographic abnormalities were less in treated hypertensives with BP control than in patients with inadequate BP control, but values were still clearly greater than in normotensive subjects. This was the case regardless whether BP control was assessed by office, home, and/or ambulatory values. Our data provide evidence that in the hypertensive fraction of the population, cardiac structural alterations can be frequently found in both the presence and absence of antihypertensive treatment. They also imply that even effective treatment of hypertension does not allow complete reversal of the cardiac organ damage characterizing high BP states.