This study is aimed to determine the predictors of nongravid vascular thrombosis in systemic lupus erythematosus (SLE) patients with positive antiphospholipid antibodies (SLE-aPL). A cohort of 67 SLE-aPL patients who had at least one positive test for lupus anticoagulant (LA), anticardiolipin (aCL), or anti-beta2glycoprotein-1(B2) was examined. Main outcome was the presence of vascular thrombosis. Association between thrombosis and risk factors was examined by contingency table. The odds ratio (OR) of significant predictors was determined by logistic regression. Three percent of patients were LA(+), 6% were aCL(+), 31% were B2(+), 3% were aCL(+)LA(+), 35.8% were aCL(+)B2(+), 7.5% were LA(+)B2(+), and 13.4% were positive for all tests. As for clinical manifestations, 79% had lymphopenia, 76% had lupus nephritis (LN), 41.8% had autoimmune hemolytic anemia, 34.3% had thrombocytopenia, 20.9% had abortion, and 19.4% had Raynaud's phenomenon (RP). Thrombosis occurred in 26 patients. The prevalence of thrombosis for SLE-aPL was 38.8%. Thrombosis was observed more frequently in patients with LA(+) (12 of 18) than the others (14 of 49; p = 0.01). Two-by-two table showed that oral contraceptive and LN were significantly associated with increased risk of thrombosis, while lymphopenia and antimalarials were significantly associated with decreased risk of thrombosis. Multivariate analysis confirmed that LN and RP were associated with increased risk of thrombosis (OR = 6.2 and 3.2; p = 0.005 and 0.008), while lymphopenia and antimalarials were associated with decreased risk of thrombosis (OR = 0.86 and 0.18; p = 0.02 and 0.034). LA is the strongest test to determine the risk of thrombosis in SLE-aPL. The presence of LN and RP strongly predicts thrombosis, while lymphopenia and antimalarials are protective. These findings help to identify patients who may benefit from prophylactic therapy.