A case of classical factor X deficiency is reported. The propositus is a 28-year-old male who presented easy bruising, epistaxis, hematomas, hematuria and occasional hemartrosis since early childhood. The severely prolonged prothrombin time was corrected by normal serum but not by adsorbed normal plasma. The abnormality was not corrected by the plasma of a patient with factor X deficiency, but by the plasma of patients with factor II or VII deficiencies. Partial thromboplastin time, prothrombin consumption and the thromboplastin generation test were abnormal. The thromboelastogram showed a prolonged ‘K’ and ‘r’ together with a normal ‘ma’. Factor X was very low (<1%). Platelet tests were normal. No factor X band or precipitates were seen on electroimmunoassay and on the cross-over electrophoresis. The non-consanguineous parents and several other members of the family were found to be heterozygotes.