Vascular access thrombosis is one of the major causes of morbidity in patients maintained on chronic hemodialysis. Thrombophilia has been recognized as a risk factor of vascular access thrombosis. The authors report a case of inherited protein S deficiency associated with vascular access thrombotic events. DNA sequence analysis of the PROS1 gene identified a novel heterozygous nonsense mutation in exon 10 by transition of AAG (lysine) to TAG (stop codon) at codon 473 (c.1417A>T, p.K473X). Results from the study suggest that the inherited protein S deficiency due to a PROS1 gene mutation may cause vascular access thrombosis in hemodialysis patients.