Recent reports seem to support the role of the thrombophilia and decreased fibrinolysis in the aetiopathogenesis of aseptic necrosis of bone. In the present study, haemostatic disturbances were analysed in adults (n = 49) and patients in childhood (Perthes disease) (n = 47) with aseptic necrosis of the femoral head. Fibrinolytic parameters (in vitro clot lysis, plasminogen, plasmatic plasminogen activator inhibitor-1 activity, D-dimer) along with lipoprotein (a) [Lp(a)] and fibrinogen were measured. von Willebrand factor, platelet activation and some thrombophilic factors (activated protein C resistance and factor V Leiden mutation, protein C, protein S activity) were also determined. Impaired fibrinolysis, an increased Lp(a) level along with slow clot lysis and increased platelet activation were found in adult cases. We detected five cases of factor V Leiden mutations (one heterozygotic and four homozygotic) among patients with Perthes disease. The clinical course of the heterozygous case was similar to the usual form of Perthes disease. The most severe form of Perthes disease has been observed in homozygous factor V Leiden mutation cases. The mutation of factor V Leiden per se probably does not induce the development of aseptic necrosis of bone tissue in childhood, but it does play a role in its acceleration. Homozygous factor V Leiden mutation definitely runs a more severe course. On the other hand, in adult cases, the disturbances of haemostasis, impaired fibrinolysis, elevated Lp(a) level, increased platelet activation and slight elevation of fibrinogen might have clinical relevance. Further studies should focus on proving the role of the haemostatic alterations in the pathogenesis of severe forms of aseptic bone necrosis. The use of antithrombotic drugs in order to slow the process of aseptic necrosis also has to be addressed in future surveys.