Genetic base for Leiden mutation of F.V (FVL) is a point mutation (1691 G to A) on a gene for F.V with an autosomal dominant heredity. There is 5%prevalence of FVL mutation in caucassian population. In a population of European women are there 80% of oral contraceptions users. The risk of deep vein thrombosis (DVT) among the women-FVL carriers is 30 times higher then in common population. The oral contraception ranks among risk factors for DVP. The effect of the thrombophilic risk factors is additive. In this article 2 cases of young girls with DVP and early use of OC are described. In both cases has developed ileofemoral thrombosis with embolisation to lungs shortly after OC was applicated. Both patients were cured with low-molecular heparin and later warfarinized. After this therapy the deep veins were partially recanalised. The cause of this thrombophilic state was FVL in homozygous constitution potentionated with OC.

        Key words: Leiden mutation of F.V, oral contraception, deep veins thrombosis