We report the results of a detailed examination of clinical events associated with the antiphospholipid antibody (aPL) syndrome in 96 consecutive patients with systemic lupus erythematosus (SLE) who underwent renal transplantation between January 1, 1984, and September 1, 1996. Because of the retrospective nature of our study, we developed strict definitions of clinical events considered to be associated with the aPL syndrome. We reviewed all available hospital, clinic, and outside records of the patients with SLE who underwent transplantation at our center during this time period and noted the results of three standard serological tests for aPLs, when available. Mean follow-up of the 96 patients was 62.6 months. Eighty-five of the 96 patients (88.5%) had at least one test for aPLs performed, and 25 patients (29.4%) had at least one abnormal test result. Among these 25 patients, 15 patients (60%) had clinical events associated with aPL syndrome. Ten patients (10.4%) either died of the aPL syndrome or had an aPL-associated clinical event within 3 months of transplantation. Other morbidity from the aPL syndrome in these 15 patients included: thrombotic arteriolar microangiopathy (2 patients), stroke (4 patients), ocular ischemia (7 patients), deep vein thrombosis or pulmonary embolism (6 patients), renal artery or vein thrombosis (4 patients), peripheral ischemia (1 patient), and fetal wastage (3 patients). By comparison, among the 60 patients with normal aPL test results, only 5 patients had clinical events compatible with the aPL syndrome (P < 0.0001 by chi-squared test). aPLs may be associated with significant morbidity and mortality in patients with SLE undergoing renal transplantation. This study is the first attempt to quantify the impact of aPLs on renal transplantation in a large population of patients with SLE. Further investigation of aPLs in SLE patients with end-stage renal disease is required to clarify the risks, benefits, and optimal clinical management of renal transplantation for these patients.