The insertion/deletion polymorphism (I/D) of the angiotensin-converting enzyme (ACE) gene has been associated in some studies with a higher prevalence of left ventricular hypertrophy (LVH), but few of them were performed on pharmacologically treated hypertensive patients. The present study was undertaken to determine whether ACE genotype determination could help in the identification of pharmacologically treated hypertensive patients at a higher risk of LVH. Ninety-six consecutive men with essential hypertension were selected for the study. Left ventricular mass (LVM) was assessed by echocardiography and indexed by body surface area and 82 patients were considered suitable for the study. Three groups of patients were defined on the basis of their I/D ACE genotype: DD (n = 39), ID (n = 33) and II (n = 10). There were no statistically significant differences between the three groups regarding to the severity of hypertension at diagnosis, degree of control of blood pressure or type of antihypertensive drug therapy used. No statistically significant differences were found between the three groups regarding to LVM index (total 124 +/- 31, DD 121 +/- 29, ID 127 +/- 35 and II 122 +/- 18 g/m2), relative wall thickness (total 0.5 +/- 0. 2, DD 0.5 +/- 0.3, ID 0.48 +/- 0.07 and II 0.47 +/- 0.04) or prevalence of LVH (total 34%, DD 31%, ID 39% and II 30% by Cornell criteria and total 39%, DD 33%, ID 45% and II 40% by Framingham criteria). Furthermore, the I and D allele frequency distribution was similar in the whole group of patients, in patients with LVH, and in a control group of healthy volunteers. Our data do not support that the I/D ACE genotype determination helps in identifying treated hypertensive patients at higher risk of LVH. Journal of Human Hypertension (2000) 14, 327-331