The objective of the present study was to define the risk factors for hypertension and to analyze the influence of insertion/deletion (I/D) polymorphism of the angiotensin-converting enzyme (ACE) on hypertension in pediatric renal transplant recipients. Twenty-six pediatric renal transplant recipients with stable renal function and treated with the same immunosuppression protocol were included in the study. Their mean age was 12.5 +/- 3.3 yr and mean time after transplantation was 38.5 +/- 39.8 month. Twenty-four hour ambulatory blood pressure monitoring (ABPM) was performed by SpaceLabs (90207) device. The I/D polymorphism of the ACE was determined by PCR and ACE serum level was analyzed by colorimetric method. Hypertension was present in 15 patients (57.7%) by causal blood pressure measurements and 19 patients (73.1%) by ABPM. Twenty-two patients (84.6%) were found to be non-dipper and eight of them had reverse dipping. Only time after transplantation (38 +/- 31 vs. 79 +/- 49 month, p = 0.016) and cyclosporin A trough plasma levels (206 +/- 78 vs. 119 +/- 83 ng/mL, p = 0.020) influenced the presence of hypertension by multiple logistic regression analysis. The distribution of genotypes were II = 2 (7.7%), ID = 8 (30.8%), DD = 16 (61.5%). There was no effect of ACE gene I/D polymorphism or serum ACE levels on hypertension prevalence and circadian variability of blood pressures. Hypertension was related to the time after transplantation and cyclosporin A levels. The ACE gene I/D polymorphism and serum ACE levels did not influence the blood pressure values or circadian variability of blood pressure among pediatric renal transplant patients.