The Prevalence Study was initiated in 1972 to determine the prevalence of different types of dyslipoproteinemias at ten North American Lipid Research Clinics. The Prevalence Study consisted of two screens designated as Visit 1 and Visit 2, and was conducted according to a standardized protocol in well-defined target populations. Data collection began in 1972 and ended in 1976. The median time between the two screens was 96 days. The objectives of Visit 1 were: to provide estimates of the prevalence of dyslipidemia in specified populations; to investigate the distribution of cholesterol and triglyceride; and to select participants for Visit 2. A total of 60,502 eligible participants were screened at visit 1. A 15 percent random sample (N=9,107) of all Visit 1 participants who had elevated lipids (N=6,882) or were taking lipid-altering medication (N=346) were asked to return for the Lipid Research Clinics Population Studies Visit 2 screen. The three groups of 16,335 participants represented approximately 25 percent of all subject screened at Visit 1. The objectives of Visit 2 were: to identify participants with primary or secondary dyslipoproteinemia; to determine the prevalence of lipid and lipoprotein patterns and their associations with coronary heart disease, other vascular diseases, and other risk factors for coronary heart disease; and to determine the relationships between lipids and lipoprotein patterns and selected nutritional, physiologic, and sociodemographic variables such as education and occupation of head of household, smoking, blood pressure, height, weight, triceps skinfold, Quetelet index, and sex hormone usage by females. Visit 2 procedures included an interview, a physical examination, an ECG, clinical chemistries, and one-day dietary recall.