The CATCH study initially recruited 5,106 third grade students to participate in a risk factor screening at baseline. Of these, 3645 (71%) participated in risk factor screening at the end of grade 8 when serum tHcy, folate, vitamin B6 and vitamin B12 were first assessed and 2909 (57%) students participated in the follow-up risk factor screening in grade 12. Of these students, 2445, attended both grade 8 and grade 12 examinations and provided blood at both examinations. This group constituted the study population for this report.