Hyperhomocysteinemia has recently been identified as an independent risk factor for arterial and venous occlusive disease. In particular, hyperhomocysteinemia has been associated with premature vascular disease, and may act synergistically with other risk factors. Two young patients with severe premature vascular disease, one venous and one arterial, have significantly elevated homocysteine levels. In addition to appropriate anticoagulant therapy, these patients receive B6 and folate vitamin therapy which normalizes the homocysteine levels. While this course of therapy is prudent, no prospective clinical trials have yet demonstrated that reduction of homocysteine levels correlates with a decreased cardiovascular risk.