A new family with classical factor X deficiency is described. The proposita is a 6 year old girl who presented with occasional epistaxis and a hematoma after an intramuscular injection. The main laboratory features consisted in a prolongation of partial thromboplastin, prothrombin and Stypven clotting times corrected by the addition of normal serum. Factor X activity varied between 3 and 6%. Factor X amydolytic activity was 15% of normal. Electroimmunoassay failed to show the presence of factor X antigen. No inhibitor was found in the proposita plasma. Parents and other family members showed intermediate levels of factor X activity and antigen and were considered to be heterozygotes. No consanguineity was found in the family.