The level of selected parameters of the coagulation system and fibrynolysis (prothrombin time, partial thromboplastin time, fibrinogen level, albumin C system, V Leiden factor and III antithrombin level) in 25 children who had been treated with Perthes disease was evaluated. In three children prolonged prothrombin time occurred; in one child anomalous protein C system was noted. The remaining parameters were normal in all children. The investigation results reveal that congenital disturbances of the haemostasis system were not the cause of Perthes disease in 24 children.