Anticardiolipin antibodies (aCL) of immunoglobulin (Ig) G and M classes were determined in 28 patients affected with chronic discoid lupus erythematosus (CDLE), comparing their prevalence and levels to those in 60 healthy subjects matched for age and sex. A high and significant frequency of IgG (67.8%) and IgM (50.0%) aCL together with prevalence of high antibody levels was found in CDLE patients, while healthy controls had IgG and IgM aCL in 1.6% and 3.3% of cases respectively. Clinical features in keeping with the diagnosis of antiphospholipid syndrome were found in one patient (3.5%), which, as the first manifestation of the syndrome, showed a pulmonary thromboembolism which appeared some days after prolonged exposure to the sun. These results provide additional data on autoimmune phenomena in CDLE and suggest that aCL test should be considered as useful aids in immunological diagnosis of CDLE.