RESUMEN
Incidences of pulmonary thromboembolism markedly increase with age. Risk factors of pulmonary thromboembolism are surgery, trauma, acute medical illness, immobilization, pregnancy, usage of hormone, and advanced age. In the cases of thrombomembolism occurred in young age, the possibility of thrombophilc state is needed to be investigated. Among many diseases or state associated thrombophilic state, homocyteinemia should be considered a cause of thromboembolism before fifth decade. Homocyteinemia is caused by deficiency of N-5-methyltetrahydrofolate, cystathionie beta-synthase and vitamin B12. The presence of the mutation of 5,10-methyleneterahydrofolate lead to homocyteinemia by deficiency of N-5-methyltetrahydrofolate. Homocysteine is acknowledged the risk factor of cardiovascular event, and storke. Homocysteinemia can be the cause of thromboemboism via damaging endotheial cell. We present two cases of pulmonary thromboembolism in young age which seem to be associated with homocysteinemia precipitated by mutation of 5,10-methyleneterahydrofolate.