The etiologic role of thrombotic and fibrinolytic disorders in Perthes' disease has not been determined. A case control study was conducted to determine whether thrombotic and fibrinolytic disorders are associated with Perthes' disease. Twenty-six patients with Perthes' disease were matched with 26 control patients for gender, age (2-year range), and time of presentation (1-year range). Thrombotic disorders were investigated for protein C activity, protein S activity, antithrombin III, anticardiolipin antibody immunoglobulins G and M, and lupus anticoagulant. Fibrinolytic disorders were investigated for tissue-plasminogen activator, plasminogen activator inhibitor-1, plasminogen activator inhibitor-1 to tissue plasminogen activator ratio, lipoprotein (a), and plasminogen. The activity of protein C, which suppresses factor Va and leads to an increase of coagulant activity when decreased, was increased in patients. There were no significant differences in the levels of other factors between the patients and controls. No evidence was found to prove a relationship between Perthes' disease and thrombotic or fibrinolytic disorders in the patients in the current study.