To determine the predictive value of the IgG anticardiolipin antibody (ACA) test for thrombosis, recurrent fetal loss, and thrombocytopenia, the clinical features of 121 patients with varying antibody levels were studied. When patients were grouped into high-positive, low-positive, and normal groups according to their ACA levels, there were strong statistical correlations with arterial thrombosis, venous thrombosis, fetal loss, thrombocytopenia, and a positive Coombs' test. At levels of 7 SD and above, the test was highly specific (greater than 80%) and predictive (greater than 70%) for thrombosis, thrombocytopenia, and recurrent fetal loss. This study suggests that the IgG ACA test may be a useful predictor for thrombosis, recurrent fetal loss, and thrombocytopenia in patients with autoimmune disorders.