Background. - Very late thrombosis of drug eluting stents is a rare complication that might be triggered by resistance to platelet antiaggregants (PAAs). Aim. - Following an initial case where clinical data strongly suggested resistance to PAAs, we carried out a prospective systematic analysis of platelet aggregation in four subsequent cases of late thrombosis. Methods. - Resistance to aspirin was investigated with the PFA-100 test employing a collagen-epinephrine cartridge (Platelet Function Analyzer; Dade Behring). Resistance to Clopidogrel was determined by flow cytometry of intraplatelet vasodilator-stimulated phosphoprotein (VASP) phosphorylation. Results. - All four cases showed resistance to either aspirin or clopidogrel, and two cases showed dual resistance to both of these PAAs. Conclusion. - Analysis of platelet function in a patient with late stent thrombosis is useful and may allow adaptation of subsequent patient management. The value of monitoring platelet function after implantation of a drug eluting stent should be evaluated in prospective studies. © 2008 Elsevier Masson SAS. All rights reserved.