The coagulation system always keeps the blood in a fluid state and is therefore incessantly active throughout life. However, the moment an injury to the vascular system occurs, the coagulation system immediately rotates 180° and transforms the blood into a perfectly localized solid body, which we call a clot. This process, by which a clot forms, is known as hemostasis, which is one of the components of the coagulation system. The importance of the Leiden mutation of factor V is based on the following: coagulation factor V is a protein that is synthesized in the liver and the gene that encodes it is located in region 23 of the long arm of chromosome 1, this factor circulates in peripheral blood inactively until it interacts with activated factor X forming a complex that converts factor II (prothrombin) into thrombin, which will have its action on fibrinogen turning it into fibrin. The regulation of activated factor V is given by the activity of activated protein C, when factor V has a mutation (named Leiden) that is caused by the exchange of an adenine for a guanine in the nucleotide 1691 of factor V (G1691A), which causes arginine to be replaced by a glutamine in the 506 residue of the factor V protein, the resulting protein is an abnormal factor V, which cannot be inactivated by activated protein C, so factor V remains activated and cannot prevent the clotting process from stopping. In our country (considering several conditions) it has been described in various publications of Mexican researchers that Leiden mutations of factor V and G20210A of prothrombin are not frequent, as they are in European countries. Keywords: Thrombophilia; factor V Leiden; coagulation disorders; Mexico