A 6 year 6month-old boy was admitted with complains of severe spontaneou epistaxis and easy brusability. He was one of five siblings, and two of them died of recurred severe epistaxis at their age of six years. There was no history of bleeding tendency to his antecedents and parents, whose marriage was unrelated. Platelet count and partial thromboplastin time were noraml with prolonged bleeding time, but clot retraction was poor. Platelet adhesion(Salzman method) was decreased and platelet aggregation test showed flat curve with no response to epinephrine and ADP. These tests of other were normal. Diagnosis of thrombasthenia was made with the above history and laboratory results.