Plasma total homocysteine (tHcy), vitamin B-12 and folate were determined in 68 patients with documented deep venous thrombosis (DVT) and in 106 age- and sex-matched healthy subjects as controls. Plasma tHcy concentrations were significantly higher (p<0.001) in patients with any DVT [median (25(th)-75(th) percentile interval)] [ 12.9 (9.9-18.4) mumol/l] and patients with idiopathic DVT [13.5 (11.0-18.1) mumol/l] in comparison to controls [10.6 (9.5-12.3) mumol/l]. No differences were observed for vitamin B-12 and folate means concentrations between patients and controls. Hyperhomocysteinemia was significantly associated (p<0.001) with any DVT (OR, 6.82; 95% Cl, 3.11-10.81) as well as with idiopathic DVT (OR, 7.40; 95% Cl, 3.01-10.81). These associations persisted after adjusting for several known risk factors for thrombosis. Using multivariate analysis, hyperhomocysteinemia was found to be positively associated with severe obesity and creatinine levels, and inversely associated with vitamin B-12 levels and thrombosis recurrence in DVT patients.