Intruduction: Fistula thrombosis in patients onmaintenance hemodialysis is an importantmorbidity factor. Arterial or venous thromboticevents have been described as complications inpatients on regular hemodialysis and positivetiters of anticardiolipin antibodies (ACLA).This study was designed to evaluate theprevalence of ACLA in hemodialysis patients andit's relation to arteriovenous fistula (AVF)thrombosis.Methods: 218 patients with AVF on maintenancehemodialysis were studied prospectively duringa period of 14 months for any episode of AVFthrombosis (AVFT), after ACLA was assayed byELISA in 171 ones. Other risk factors forthrombosis such as presence of diabetes,hypotension during dialysis, using oferythropoietin (rEpo), fistula site, gender,age, dialysis duration, and type of dialysermembrane were accessed.Results: 56% of the patients had IgG ACLA = 10 GPL whichwas significantly correlated with dialysisduration (23.18 ± 24.56 months in patientswith ACLA = 10~GPL vs 37.73 ± 36.35 months inpatients with 20 = IgG ACLA < 40 GPL). Within 14months follow up, 39 episodes of AVFT occurredin 34 patients (15.8%). Dialysis duration priorto start of study was 29.16 ± 22.04 months.In our patients radiocephalic AVFs showed morethrombosis than brachiocephalic ones (23% vs10%, p = 0.01 by Chi-square). Age more than 50years old was a risk factor for AVFT (p = 0.034by Chi-square). Also erythropoietin use(p = 0.011 by chi-square) and ultrafiltrationmore than 3 liters (average value of 14 months)were correlated with AVFT (p = 0.042 byChi-square), but there wasn't any correlationbetween diabetes, presence of ACLA, hypotensionduring dialysis, gender, and dialysis membraneswith AVFT. Ultimately, logistic regressionanalysis of factors associated with thrombosiswas done and only fistula site (p = 0.015,O.R. = 2.87), and Eprex use (p = 0.031, O.R. = 4.05)showed significant correlation with AVFT.Conclusion: Although incidence ofanticardiolipin antibodies was high in ourpatients, we found no correlation between IgGACLA and AVFT. Instead, we found thatradiocephalic fistulas and Eprex injection wererisk factors for AVFT.