Behcet's disease (BD) is a chronic, multi-systemic and inflammatory disorder. The local renin-angiotensin system (RAS) in the vessel wall plays a role in the endothelial control and contributes to inflammatory processes. Angiotensin-converting enzyme (ACE) is the regulatory component of the RAS. This study was conducted in Turkish patients with BD to determine the frequency of I/D polymorphism genotypes of ACE gene. Genomic DNA obtained from 566 persons (266 patients with BD and 300 healthy controls). ACE gene I/D polymorphism genotypes were determined using polymerase chain reaction using I and D allele-specific primers. There was statistically significant difference between the groups with respect to genotype distribution (p < 0.001). This study is the largest study in Turkish population that ACE gene I/D polymorphism investigated in BD. As a result of this study, ACE gene I/D polymorphism DD genotype could be a genetic marker in BD in Turkish study population.