LANZMANN’S THROMBASTHENIA is a well-G defined inherited disorder of platelet function.’.” It is caused by a deficiency or abnormality of the membrane glycoprotein (GP) IIb-IIIa complex with bleeding due to defective platelet hemostatic plug formation. Thrombasthenia has achieved much recognition for such a rare disease because it has been important in defining GP IIb-IIIa as a platelet receptor for fibrinogen and other adhesive proteins, and it has provided a model for understanding the molecular basis of platelet aggregation. Thrombasthenia is also familiar from a clinical perspective because the diagnosis must be considered in patients presenting with the common problems of purpura, a normal platelet count, abnormal platelet aggregation, and a long bleeding time. I2 Although the membrane GP abnormalities of Glanzmann’s thrombasthenia have been carefully studied5-” and genetic defects are being de~ cribed,’~-’~ the clinical aspects of the hemorrhagic disease are not well-documented. In this review the data on 177 patients are analyzed: previously published data on 113 patients are supplemented with the description of 64 patients who have been studied in Paris over the past 33 years. The opportunity to observe the nature and severity of the bleeding manifestations among these 177 patients has allowed us to define the clinical spectrum of thrombasthenia. The opportunity to follow the 64 patients in Paris for many years has provided data on the course and prognosis of the hemorrhagic disease. These observations provide a basis for discussing the management of patients with Glanzmann’s thrombasthenia and other disorders of platelet function.