Objectives - The aim of our study was to evaluate the prevalence of antithrombin, protein C and protein S deficiencies in consecutive ischemic stroke patients under 45. Material and methods - We studied 127 consecutive patients with a mean age of 34.4 years admitted for an ischemic stroke, over a 2-year period, after exclusion of those with arterial dissection. Antithrombin, protein C and protein S levels were measured in all patients at the acute stage of the ischemic stroke and measurements were repeated in case of abnormality. Results - We found abnormal levels in 9 patients. Seven had an acquired cause of deficiency (pregnancy, oestrogen, acute inflammation). Two had no obvious acquired cause of deficiency but further controls were normal. Conclusions - Hereditary deficiencies of coagulation inhibitors are rare in ischemic stroke patients under 45 and their systematic detection seems to be of poor interest.