['To evaluate the effects of plasma total homocysteine (tHcyt) and the MTHFR 677C>T polymorphism on determining the intracranial- (IC) and extracranial (EC) locations of atherosclerosis.', 'Brain MR angiography was performed on 463 patients with symptomatic ischaemic stroke to detect significant atherosclerosis (more than 50% stenosis of vessel diameter) in the IC- and EC arteries. Relationships between IC- or EC atherosclerosis and plasma tHcyt level and/or MTHFR 677C>T genotypes were analyzed after adjusting for vascular risk factors.', 'The odd ratios (ORs) of plasma tHcyt were not significantly higher in patients with either IC- or EC atherosclerosis than in patients with no atherosclerosis. When the study subjects were stratified into three subgroups according to their plasma tHcyt levels, neither the crude ORs nor adjusted ORs of each IC- and EC atherosclerosis in highest and middle plasma tHcyt tertile were significantly different from those in lowest plasma tHcyt tertile. The ORs of the MTHFR 677TT genotype in IC- and EC atherosclerosis were not significantly different from those in no atherosclerosis. There was no dose-dependent effect of MTHFR 677T allele on either IC- or EC atherosclerosis.'] Do plasma total homocysteine and the methylenetetrahydrofolate reductase 677C > T polymorphism contribute to the distribution of cervico-cerebral atherosclerosis in ischaemic stroke patients?