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="">