Disorders of hemostasis are frequently encountered, and, if not recognised as early as possible, in particular prior to surgery, may lead to bleeding complications which are much more difficult to treat than those where exact diagnosis permits specific preventive therapy. A first case report on a woman with an acquired inhibitor against factor VIII illustrates that even minor injury may lead to hemorrhage necessitating blood transfusion. Furthermore, as long as the defect remains inaccessible to successful substitution therapy, wound healing will not take place. A second case report describes a patient with a congenital dysfunction of blood platelets, and serves as an example for similar disorders which, if unrecognised, lead to multiple, otherwise avoidable complications. Unfortunately there is no clearcut correlation between a given defect of hemostasis and bleeding manifestations, since psychological factors, among others, appear to influence the occurrence of "spontaneous" hemorrhage. Any unexpected and unexplained bleeding complication requires careful evaluation of the possible underlying causes, since such investigations often not only affect the future of the propositus himself but also that of his family members.