OBJECTIVE: Antiphospholipid antibodies (aPL), namely anticardiolipin antibodies (aCL) and lupus anticoagulant (LAC), have been associated with an increased risk of thrombosis in systemic lupus erythematosus (SLE). We examined additional thrombosis risk factors (aPL profile, SLE-related, and traditional risk factors) and the primary thrombosis prevention in SLE patients with and without aPL. METHODS: All SLE patients with positive aPL but without previous thrombotic manifestations who were regularly followed up at our department (n = 144) and 144 age- and sex-matched SLE patients with negative aPL were included in this study. The median followup times were 104 and 112 months, respectively. The demographic, clinical, laboratory, and treatment characteristics and the traditional thrombosis risk factors were recorded. RESULTS: The thrombosis rate was 29 per 144 aPL-positive patients (20.1%) and 11 per 144 aPL-negative patients (7.6%; P = 0.003). In multiadjusted analysis, significant predictors of thrombosis were male sex (hazard ratio [HR] 6.25, P < 0.01), LAC (HR 3.48, P = 0.04), and constantly positive aCL (HR 5.87, P = 0.01) for aPL-positive patients, while male sex (HR 7.14, P = 0.03) and hypertension were predictors for aPL-negative patients (HR 6.49, P = 0.03). Additionally, the duration of low-dose aspirin treatment played a protective role against thrombosis in aPL-positive patients (HR per month 0.98, P = 0.05), as did the duration of hydroxychloroquine in both aPL-positive (HR per month 0.99, P = 0.05) and aPL-negative patients (HR per month 0.98, P = 0.04). CONCLUSION: Independent predictors of thrombosis for aPL-positive patients were male sex, LAC, and constantly positive aCL, and for aPL-negative patients were male sex and hypertension. The duration of low-dose aspirin use played a protective role against thrombosis in aPL-positive patients as did the duration of hydroxychloroquine in both groups.