OBJECTIVE Previous studies have documented a high frequency of thrombotic events in lupus nephritis patients with antiphospholipid (aPL) antibodies in the serum, but there is little information on the impact of serum aPL antibodies on the clinical outcome of lupus nephritis. The aims of this study were to evaluate the seroprevalence of aPL antibodies in patients with lupus nephritis and assess their prognostic value in relation to long-term renal outcomes. METHODS A retrospective analysis was undertaken in 49 patients with lupus nephritis who underwent renal biopsy. The serum aPL antibodies were monitored regularly in the patients who were followed up for a mean of 76.4+/-47.2 months, and possible factors associated with the long-term renal outcomes in these patients were analyzed. RESULTS The overall seroprevalence of aPL antibodies was 41%. During the follow-up, 40% of aPL antibody-positive patients experienced thrombotic events. The frequency of class V lupus nephritis was lower in the aPL antibody-positive patients (6 out of the 20 aPL antibody-positive vs. 14 out of the 29 patients aPL antibody-negative patients; p=0.03). A multivariate analysis identified age (p=0.0001), eGFR at presentation (p=0.0015) and presence of hypertension (p=0.0025) as independent risk factors for the development of chronic kidney disease (CKD) with eGFR less than 60 ml/min/1.73 m(2). CONCLUSIONS Detection of aPL antibodies in the serum of patients with lupus nephritis is useful to identify patients at risk of thrombotic events. Hypertension is associated with the probability of CKD with eGFR less than 60 ml/min/1.73 m(2).