Here, we diagnosed a Turner syndrome patient complicated with well differentiated hepatocellular carcinoma. The patient had an extremely high level of plasma fibrinogen. However, her clinical features and coagulation test abnormalities were quite different from those reported cases. We investigated the mechanisms underlying the hyperfibrinogenemia and its effects on coagulation tests. Plasma fibrinogen was analyzed by Clauss, immunoturbidimetry and Western methods. The fibrinogen genes were sequenced. Activated partial thromboplastin time, prothrombin time and thrombin time were measured. Fibrinogen expression in tumor tissues was examined immunohistochemically. Plasma cortisone, interleukin 6 and soluble tissue factor were measured by immunoassays. We found that abundant fibrinogen protein was detected in tumor cells. Plasma fibrinogen activity and antigen were 14.4 +/- 0.8 and 15.1 +/- 0.3 g/l, respectively. On SDS-PAGE, patient and control fibrinogen subunits migrated similarly. No mutations were found in the fibrinogen genes. Activated partial thromboplastin time, prothrombin time and thrombin time were significantly prolonged, but were normalized when fibrinogen was partially absorbed by an antifibrinogen antibody. Plasma interleukin 6, cortisone and soluble tissue factor levels were increased as compared with those of controls. After tumor resection, plasma fibrinogen level and other laboratory tests returned to normal. Our results showed that the hyperfibrinogenemia was caused by hepatocellular carcinoma. High levels of plasma cortisone and interleukin 6 may also contribute to the hyperfibrinogenemia. With the increase of levels of plasma fibrinogen, the values of activated partial thromboplastin time, prothrombin time and thrombin time were gradually prolonged, probably due to the effect of fibrin on thrombin (antithrombin I) and restricted fibrin polymerization by superfluous fibrinogen.