Thirty-five patients with the lupus anticoagulant (LA) were followed up between 1975 and 1982. The most prevalent clinical manifestation occurring in these patients was thrombosis. Nineteen patients (54.3%) had a single or recurrent thrombotic episode. Fifteen patients (42.8%) had venous thrombosis, and arterial thrombosis manifested by stroke or transient ischemic attacks occurred in six patients. Bleeding occurred in only five patients, four of whom had severe thrombocytopenia, while no excessive bleeding was noted during 18 operative procedures. Various therapeutic regimens, including corticosteriods, nonsteroidal anti-inflammatory drugs, cytotoxic or immunosuppressive agents, had no effect on the presence of the LA in these patients. Anticoagulants were successful in the treatment and prevention of thrombotic episodes.