Introduction Regulation of angiotensin converting enzyme (ACE) and angiotensin II (ang-II) levels is under genetic control. 1,25(OH)(2) vitamin D-3 treatment has shown to reduce the ang-II level, reduce myocardial hypertrophy and to decrease blood pressure. This study was designed to examine the effect of ACE gene polymorphisms on 24-h ambulatory blood pressure measurement (24 h) values, vitamin D levels and target organ damage in hypertensive patients.,Methods This study was carried on 118 patients with essential hypertension (female/male: 70/48, mean age: 49.1 +/- 7.6 years, hypertension duration: 56 +/- 40.5 months). All patients were assessed for target organ damage; the eye by retinal examination, the heart with echocardiography and the kidney with blood and 24-h urine analysis. 24-h ambulatory blood pressure measurement was performed in all patients. PCR amplification was employed to detect ACE genotypes.,Results ACE genotypes were as follows: DD (n=49) 41.5%; ID (n = 37) 31.4% and II (n = 32) 27.1%. No difference was present between groups of ACE polymorphism when 24-h ambulatory blood pressure measurement values, retinal vascular changes and microalbuminuria were taken into account. Statistically significant left ventricular mass index levels were obtained in the DD group when compared with the non-DD (ID + II) group (P:0.009). Positive correlations have been noted between left ventricular mass index and day/night and early morning systolic pressures. A negative correlation exists between serum 25 (OH) vitamin D levels and 24-h ambulatory blood pressure measurement values (P < 0.05).,Conclusions The presence of the D allele is linked with a higher risk for left ventricular mass index in the Turkish hypertensive population. Blood Press Monit 12:207-213 (C) 2007 Lippincott Williams & Wilkins.