Vascular access occlusion is frequently seen in some patients on hemodialysis. There are different opinions about pathogenesis of recurrent access thrombosis. Anticardiolipin (aCL) antibodies have been suggested to be involved in thrombosis and can be found in a high proportion of patients with chronic renal failure. We investigated the relationship between vascular access occlusion and the level of aCL antibodies in hemodialysis patients. We measured serum IgG and IgM aCL antibodies and protein C levels in 50 patients on hemodialysis having no fistule thrombosis (group 1), in 33 patients on hemodialysis with fistule thrombosis (group 2), and 20 nondialyzed patients with chronic renal failure (group 3). There were no differences in age and duration on hemodialysis (p > 0.05). No significant correlation was found between protein C and platelet counts in all groups (p > 0.05). In group 1, aCL IgG and IgM were 2%. In group 2, aCL IgG and IgM, were 6.06% and 0%, respectively. In group 3, aCL IgG and IgM were negative. We did not find any significant difference between aCL IgG and IgM in all groups (p > 0.05). No association was found between aCL antibodies and vascular access thrombosis in our patients on hemodialysis.