Studies on hyperhomocysteinemia in vascular occlusive disease have included mostly patients with arterial occlusion. However, more recent studies have included cases of venous occlusive disease as well. Our present study is aimed at comparing the prevalence of hyperhomocysteinemia in venous occlusive disease vis-à-vis arterial occlusive disease in the North Indian urban population. Homocysteine was estimated by chemiluminescent immunoassay in 205 normal controls and 536 patients, 244 presenting with arterial occlusion and 292 with venous thrombotic disease. The mean homocysteine in patients with arterial occlusion was 21.79 +/- 0.09 micromol/L (mean +/- standard error of measurement), in patients with venous thrombosis was 25.53 +/- 0.1 micromol/L, and in controls was 11.33 +/- 0.18 micromol/L. The prevalence of hyperhomocysteinemia (> 15 micromol/L) was 56.38% in arterial occlusive disease and 54.64% in venous thrombosis. In patients with peripheral vascular occlusive disease, patients with deep venous thrombosis (DVT) had the highest mean homocysteine level (25.51 micromol/L), which was even higher (32.14 micromol/L) when associated with pulmonary embolism (PE). There is a high prevalence of hyperhomocysteinemia in arterial and venous occlusive disease. Hence, in all patients with vascular occlusive disease, hyperhomocysteinemia should be elucidated and treated. In addition, long-term follow-up is required to ascertain whether the reduction in homocysteine decreases the thrombotic events and whether homocysteine levels can actually be of prognostic or predictive value in cases of DVT with PE.