The May-Hegglin anomaly is one of the rare forms of heriditary thrombocytopenia. Since fewer than 100 cases of May-Hegglin anomaly have been described to date, major controversies regarding the adequacy of hemostasis in vivo and abnormalities of platelet function in vitro continue to prevail. This report describes the results of coagulation, platelet function, platelet ultrastructure, and survival studies performed for a family with six previously unreported cases occurring in three generations. One member of this family also had frequent epistaxis and a prolonged bleeding time associated with cyanotic heart disease that required open heart surgery for correction. The laboratory assessment of hemostasis in such patients before major surgery is also discussed.