Cerebral infarction is a rare pathology among children and its etiology can be identified in almost two-thirds of cases. The remaining one-third are considered idiopathic. Recently, inherited disorders of blood coagulation predisposing to thrombosis have been taken into account as a possible cause of childhood stroke. We describe here a case of a 6-year-old child presenting with ischemic stroke and protein S (PS) defect. The family study suggested inheritance of the defect. The immunological characterization of PS in the affected family members was consistent with a defect mainly in the free form of PS. In the case here reported no associated predisposing condition to stroke could be identified but familial PS defect was found. No therapy was administered. Nevertheless symptoms disappeared spontaneously and there were no recurrences at the 1 year follow-up. Diagnostic imaging techniques demonstrated that a reduction in the cerebral ischemic area had occurred 2 months after the stroke.