The role of endothelial nitric oxide synthase gene intron 4 a/b (eNOS4a/b) variable number of tandem repeats (VNTR) polymorphism in various renal diseases was investigated. We investigated whether the eNOS4a/b VNTR polymorphism is associated with susceptibility to acute poststreptococcal glomerulonephritis (APSGN) and its clinical features. Endothelial NOS4a/b VNTR polymorphism is determined by the polymerase chain reaction in 60 children with APSGN, and 66 healthy controls. The genotype distribution of eNOS4 does not differ between the patients and the controls (X(2)=5.1, p=0.079). However, the frequency of eNOS4a (eNOS4a/a and eNOS4a/b) genotype is higher in the patients than in the controls (X(2)=4.5, p=0.046). In the APSGN group we performed renal biopsy on eight patients because of nephrotic syndrome accompanies acute nephritic syndrome or glomerular filtration rate (GFR) is lower than 50% of normal, and found that to carry a/a and a/b genotypes were a significant risk factor for this type presentation (OR=17.3, 95% CI:1.95-152.67, p=0.03). Mean serum creatinine values are found statistically significantly higher in a/a and a/b genotypes when compared with b/b genotypes (p=0.022). Children carrying the "aa" and "ab" genotype or "a" allele of eNOS4 have a greater tendency to develop and clinical presentation of APSGN.