Abstract: Anti-cardiolipin antibodies (ACA) occur in patients with SLE, lupus-like illness and with some other illnesses, such as malignancy, syphilis and among healthy elderly. We found that the prevalence of IgG and IgM ACA isotopes in 147 Iranian SLE patients was 49.7% for IgG and 5.6% for IgM. In addition, some SLE and non-SLE patients from other centers were studied: the prevalence of ACA-IgG in SLE patients from Mashad was 54%; ...