Increased levels of IgG anticardiolipin antibodies (ACA) were found in 23 of 98 patients (23%) with systemic lupus erythematosus. Increased levels of IgM ACA were found less frequently (5%). All four patients with major cerebrovascular events had increased IgG ACA, including the two with highest levels, both of whom were men. Six of nine patients with livedo reticularis had increased IgG ACA. In turn, this clinical feature was associated with cerebrovascular disease in two and renal disease in another six. IgG ACA were not associated with other thromboembolic events, thrombocytopenia, serum IgG, or autoantibodies to Ro(SSA), La(SSB), U1RNP, Sm, or double or single stranded DNA.