RESUMO
INTRODUCTION: Venous thromboembolic diseases have an incidence of 1.57/1000. Among patients under 50 years old, thrombophilia is assessed, the indications for which are increasingly stringent. Today, the need of plasma homocysteine assay is uncertain. OBSERVATION: Our case is a 42 year-old man, in whom a pulmonary embolism associated with macrocytosis made us discover a B12 deficiency secondary to Biermer's disease. In the literature, patients are men with an average age limit to the realisation of the assessment of thrombophilia. Not all of these patients had any causal other than hyperhomocysteinemia secondary to Biermer's disease. The support is not detailed. CONCLUSION: Hyperhomocysteinemia is probably not the only thromboembolic factor. The patient received anticoagulation and vitamin B12 supplementation. A good reading of the complete blood count is essential.