A predisposition to thrombosis in patients with procainamide-induced lupus anticoagulants is previously unrecognized. We describe two patients treated with procainamide who experienced acute thromboembolic events temporally associated with development ofthe lupus anticoagulant. One patient had a deep venous thrombosis and pulmonary embolism, while the other patient had a cerebrovascular accident. In both patients, coagulation parameters corrected with interruption of procainamide therapy. We suggest that thrombosis may complicate treatment with procainamide in patients who develop the lupus anticoagulant.