IgA nephropathy(IgAN) is the most common glomerulonephritis(GN) in worldwide, and accounts for 20% to 40% of all patients with primary GN in Korea. IgAN has diverse clinical courses, but the risk factors affecting the deterioration of renal function are not established. Recently, there were some suggestions that systemic or local expression of peptides of angiotensin system exerts several effects on the progression of renal disease, and the genetic polymorphisms may associated with peptide expression. To evaluate the role of genetic polymorphism of angiotensin I converting enzyme(ACE) polymorphism in the progression of IgAN, the genotypic distributions in 278 biopsy-proven cases of IgAN were studied, which had undergone a renal biopsy at Seoul National University Hospital, between 1979 and 2000. We also compared the genotypes with clinical manifestations to evaluate the clinical implications of genetic polymorphism. The study shows that there was no difference in the ACE genotype frequencies between the patients (II : 26.6%, ID : 55.0%, DD : 18.4%) and normal controls(II : 31.4%, ID : 57.4%, and DD : 11.2%). Seventy- two percent and 48% of patients maintained renal function for 10 years and 20 years after the initial diagnosis in 278 patients, respectively. However, in 153 patients who were followed more than 5 years, the DD genotype was more prevalent in patients with deteriorating renal function than in those with stable renal function(31.8% vs. 13.8%; p=0.0146). Presence of systemic hypertension increased the risk of renal disease progression(OR=3.3), and it was showed 7.4 fold risk whenever the creatinine was increased by 1 mg/dL. Renal disease progression is not associated with DD genotype among normotensive patients at the biopsy. But, in patients with hypertension, II and DD/ID genotypes have an increased risk for disease progression when compared with II genotype of normotensive patients(OR=1.4, OR=7.8; respectively). ACE polymorphisms did not have any interaction with the levels of serum creatinine at the time of biopsy in our patients. Our results suggested that ACE genotypes(D allele) affected the progression of IgAN, especially in hypertensive patients. One of the prospects of the present study is the potential for screening high risk individuals, thus helping to develop a practical application of the molecular findings in clinical practice.