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Coronary heart disease tends to run in families, and the familial resemblance of major risk factors for the disease was examined among various types of adult family members. Family units were assembled from a total of 4,738 men and women who took part in a cross sectional health survey in four Norwegian municipalities where all inhabitants between 20 and 52 years of age were invited. After adjusting for age and other confounders, correlation coefficients were derived as a measure of the degree of resemblance. Viewed across all types of investigated familial relationships, similarity was found to be stronger for total cholesterol than for high-density lipoprotein cholesterol and triglycerides, and also stronger for systolic than for diastolic blood pressure. Between husbands and wives (3,060 subjects), correlations were small (between 0.02 and 0.06), except for 0.11 for total cholesterol. Lipid and blood pressure correlations ranged from 0.13 to 0.27 for parents and their offspring (471 subjects, p < 0.05) and from 0.11 to 0.22 among siblings (2,166 subjects, p < 0.01). Sibling correlations were consistent across age groups. Furthermore, reports from each individual on daily smoking (yes or no) revealed that husbands and wives had similar habits in 63.5% of all marriages as compared with the expected 49.4% had no smoking similarity at all been present. Smoking concordance was also demonstrated among siblings (p < 0.01). The persistent pattern of lipid and blood pressure aggregation among genetically related individuals from 20 to 52 years of age and the much weaker such similarity between husbands and wives, point towards genes or commonly shared environment at early ages as a major reason why coronary heart disease runs in families.