The aim of this unique study was to consider the relationship between folate and vitamin B(12) on homocyst(e)ine (Hcy) concentration in an apparently healthy cohort of Welsh young people. A cohort of 179, 12-13 year olds (88 boys and 91 girls) were measured for Hcy, folate, vitamin B(12), adiposity, and dietary habits. Boys had significantly higher waist circumference and folate concentration than girls. Folate was negatively associated with Hcy in both sexes, whereas vitamin B(12) was negatively associated with Hcy in boys only. Adiposity was not associated with Hcy. Folate was an independent predictor of Hcy in both sexes, whilst vitamin B(12) was an independent determinant of Hcy in boys only. Familial history of cardiovascular disease (CVD) risk factors was identified in 69% of the children with elevated Hcy (> or = 8.5 mumol.L(-1)). Young people might be encouraged to increase their folate intake through diet, particularly by increasing their consumption of leafy vegetables and fruit. Further research is necessary to determine the exact contribution of genetics and diet on Hcy levels in young people, and whether Hcy levels during childhood and adolescence might influence future CVD risk.