The authors present the case of a 18-year-old boy egamined on account of accidentally detected splenomegaly and suspected venous convolute in the region of the porta hepatis. Coeliacography revealed cavernous reconstruction of the portal vein due to an old thrombosis and thrombosis of the lineal vein. At the time of assessment of this diagnosis the Patient had no apparent risk factor for the development of venous thromboembolic disease. With regard to the serious character of the finding and the Patient s age later detailed haemocoagulation, biochemical and genetic egaminations esere made. The only risk factor for the development of thrombosis which was detected was medium severe hyperhomocysteinaemia (46.7 pmol/1) with C677T mutation in the Bene for 5,10-methylene tetrahydrofolate reductase in the homozygous state. Although hyperhomocysteinaemia was identified already in the past as an important risk factor for the development of venous thromboembolic disease, in the available literatuře so far no case of porral vein thrombosis was described in a Patient with hyperhomocysteinaemia as the only apparent risk factor.

        Key words: Portal vein thrombosis - Hyperhomocysteinaemia