Aortic dissection (AD) is a disease characterized by tear of the aortic intimal layer and separation of the arterial wall. Some risk factor such as hypertension and Marfan syndrome is well known in AD. However, the role of genetic factors in AD is largely unknown. Insertion/deletion (I/D) polymorphism of the angiotensin-converting enzyme (ACE) gene is associated with cardiovascular diseases; patients with D allele have higher serum and tissue ACE levels. We investigated the relationship between the I/D polymorphism of the ACE gene and non-syndromic acute AD. Sixteen patients diagnosed with AD were included in the study (mean age: 60.1 +/- 6.2 years). The diagnosis was established by clinical evaluation and imaging techniques. The control group consisted of 22 age-matched patients without AD (60.9 +/- 7.3 years), who suffered from chest pain. Incidence of hypertension was similar in dissection and control groups (62% vs. 59%). The I/D polymorphism was investigated in both groups by PCR analysis. Dissection types according to the DeBakey classification were identified as type 1 (proximal + distal) in 7 patients (43%), type 2 (proximal) in 5 patients (31%), and type 3 (distal) in 4 patients (25%). The D/D and D/I polymorphisms are present in 13 and 3 AD patients, respectively. None of patients with AD have the II polymorphism. The frequencies of the D allele (DD + ID) are significantly higher in dissection group than control (100% vs. 68%, P < 0001). These results indicate that the D allele of ACE gene is a risk factor for AD.