BACKGROUND:The overall aim was to test whether low birthweight (LBW) in newborns is associated with the risk indicators for cardiovascular disease in early middle age, even in a welfare society. Further, a possible interaction of LBW and heredity for myocardial infarction or stroke was investigated. METHODS:Overall, subjects were identified as newborns in a local birth register, and as adult participants, in the Västerbotten Intervention Program (n = 7876). Outcome measures such as systolic (SBP) and diastolic blood pressures (DBP), body mass index (BMI), cholesterol, triglycerides and anthropometrics were investigated (at age 29-41 years) in relation to LBW. RESULTS:Low birthweight was associated with increased SBP and DBP. Triglycerides were elevated among women with LBW and total cholesterol was elevated in men with LBW. Heredity for myocardial infarction or stroke interacted with LBW, and indicated a synergistic effect on the level of SBP. The BMI did not differ between LBW and normal birthweight subjects. CONCLUSIONS:Our interpretation is that the 'fetal origins' hypothesis' is valid for middle-age subjects who grow up in a welfare society. The population attributable proportions that result from different exposures to LBW were relatively small overall; from a public health perspective, heredity was more important than LBW for elevated SBP.