['Mild hyperhomocysteinaemia (HHC) is associated with an increased risk of premature atherothrombotic cerebrovascular disease. We investigated the clinical efficacy with regard to the incidence of cardiovascular events of treatment of mild HHC with vitamin B(6) plus folic acid.', 'We studied 224 consecutive patients with clinically manifest atherothrombotic cerebrovascular disease with onset before the age of 56. Follow-up was obtained in 203 (90.6%) patients. At baseline, 52 (25.6%) were hyperhomocysteinaemic after methionine loading and started treatment with vitamin B(6) (250 mg) plus folic acid (5 mg); 151 (74.4%) were normohomocysteinaemic (reference group).', 'During follow-up (median 57 months), 31 (20.5%) of the normo- and 11 (21.2%) of the hyperhomocysteinaemic patients had a new cardiovascular event. The crude incidence rate per person-year for any cardiovascular event was similar in both groups (0.043 [CI, 0.029-0.057] in the normo- vs. 0.045 [CI, 0.021-0. 069] in the hyperhomocysteinaemic group). Multivariate Cox-regression analyses showed that hypertension and cholesterol levels were associated with an increased risk of new cardiovascular events in the total group [relative risk [RR] (yes vs. no), 7.4 (3. 4-16.0) and RR (per 1 mmol/l), 1.9 (CI, 1.4-2.7)]. The adjusted RR for new cardiovascular events in the hyper- as compared to the normohomocysteinaemic patients was 0.96 (CI, 0.48-1.92).'] Are normohomocysteinaemia and vitamin-treated hyperhomocysteinaemia associated with similar risks of cardiovascular events in patients with premature atherothrombotic cerebrovascular disease . A prospective cohort study?