Systemic lupus erythematosus (SLE) is an inflammatory multisystem disease of unknown etiology with immunologic aberrations. Many studies have shown that genetic and environmental factors are implicated in the development of SLE. Angiotensin-converting enzyme (ACE) affects various immune phenomena through the renin-angiotensin and kallikrein-kininogen systems by creating angiotensin II and inactivating bradykinin. We investigated the correlation between insertion/ deletion polymorphism of the ACE gene and the clinical manifestations of SLE, especially vascular involvement and lupus nephritis. Two-hundred and eleven Korean patients fulfilling the ACR criteria and 114 healthy subjects were enrolled. The ACE genotype was determined by polymerase chain reaction using genomic DNA from peripheral blood. The nephritis patients were classified by the WHO classification. In addition, the activity and chronicity index were used to assess the severity of renal involvement. We evaluated vascular involvement by the presence or absence of hypertension, Raynaud's phenomenon, livedo reticularis, antineutrophil cytoplasmic antibody and the SLICC/ACR Damage Index. The gene frequency of ACE gene polymorphism was as follows: II 39 vs 34%, ID 41 vs 50%, DD 20 vs 16% in SLE patients and controls, respectively. There was no difference in genotype frequency between both groups. There were no significant differences between the distribution of ACE gene genotypes and lupus nephritis and its related parameters, including WHO classification, activity index, chronicity index, renal dysfunction and amount of 24 h urinary protein. The ACE genotypes and alleles did not affect the presence of vascular manifestations evaluated, but the frequency of DD genotype was significantly low in SLE patients with Raynaud's phenomenon compared to those without Raynaud's phenomenon (P = 0.002 for ACE ID vs DD and II, OR 2.7, 95% CI 1.43-5.09; P=0.023 for ACE DD vs ID and II, OR 0.33, 95% CI 0.12-0.89). Also skewing from DD to II genotype was noted in patients with anti-Sm antibody compared to those without anti-Sm antibody (P = 0.025 for ACE DD vs ID and II, OR 0.21, 95% CI 0.05-0.93). The onset age of serositis was older in patients with the ID genotype than the others (ID= 34.5+/-10.8, II + DD = 25.6+/-10.2, P= 0.002). Also the onset age of malar rash was older in patients with II genotype than the others (II=26.7+/-8.4, ID+DD=21.3+/-9.0; P=0.021). The patients with I allele showed a significantly higher frequency of serositis (P = 0.022). Taken together, the I/D polymorphisms of ACE gene did not affect susceptibility of SLE, lupus nephritis and the vascular manifestations, including Raynaud's phenomenon, in Korean SLE patients, although the DD genotype was negatively associated with Raynaud's phenomenon among SLE patients. However, it would be valuable to evaluate the role of other genes potentially related to vascular events, such as endothelin, nitric oxide or angiotensin II receptor as well as ACE gene.