Abstract Conflicting data from Western European and USA population studies led us to investigate hyperhomocysteinemia (HHcy), the methylenetetrahydrofolate reductase ( MTHFR) C677T polymorphisms and thrombotic disease in North Western Russia. Plasma total homocysteine (tHcy) levels, MTHFR C677T genotype, selected life style determinants and haemostatic factor activity were determined in patients with arterial ( n=33), venous ( n=40), arterial+venous ( n=11) thrombosis and healthy controls ( n=30). We found raised median tHcy levels in all patient groups vs . controls ( p<0.05), with odds ratios (95% CI) for vascular disease among patients with HHcy (defined as>15 μmol/l) of 3.9 (0.6–14.3), 4.8 (1.2–18.8) and 15.8 (2.8–87.3) respectively. tHcy levels were a function of MTHFR C677T genotype, and all patients with tHcy levels>30 μmol/l had the MTHFR C677T homozygous substitution. Elevated tHcy levels ( p<0.05) were identified in smokers and coffee drinkers, with the degree of elevation dependent on MTHFR C677T genotype. Of the studied haemostatic parameters increased factor VIII activity and vWF antigen and activity was observed in HHcy subjects. We conclude that HHcy and MTHFR C677T genotype are positively associated with arterial and venous thrombotic disease in the population of North Western Russia.