The distribution of the phenotypes for coagulation factor XIIIA subunit (F13A) of autochthonous individuals from the following five Spanish populations was studied: Galicia, Castilla-León, Castilla-La Mancha, Extremadura and Western Andalusia. The frequency values obtained for F13A*2 ranged from 0.248 to 0.311. To date, these values are the highest recorded in the world.