BACKGROUND: There is concern that the childhood epidemic of obesity will result in increases in the risk of cardiovascular disease in the future; however, there is currently little direct evidence on this issue. METHODS AND RESULTS: We assessed the association of body mass index, measured when subjects were a mean age of 4.9 years old, with the future risk of coronary heart disease (CHD) and stroke in a large Scottish birth cohort (born in the 1950s) who have been linked to hospital admissions and mortality data. At the start of the follow-up period (1981), there were 11,106 (91%) members of the cohort alive and believed to be resident in Scotland. Over the follow-up period, they contributed 245,000 person-years of risk. Among these subjects, there were 302 (53 fatal) cases of CHD, 109 (4 fatal) cases of stroke, and 397 (57 fatal) cases of either a CHD or stroke. There was no association between childhood body mass index and CHD risk. There was no linear association between childhood body mass index and stroke risk, but those who were obese in childhood (top 2.5% of the body mass index distribution) compared with all others had an increased risk of stroke; the adjusted (for gender, father's occupational social class at birth, number of siblings, and birth weight) hazards ratio was 2.41 (95% CI 1.00 to 5.86). CONCLUSIONS: Body mass index in early childhood does not appear to be associated with increased CHD risk in later life.