Since 1967 the Reykjavík study has monitored coronary artery disease and its risk factors in randomly selected cohorts. From 1979 to 1984, 3246 men and 3545 women aged 45-74 years were studied. Routine biplane chest X rays were assessed by a radiologist who noted the presence or absence of aortic calcification (AC), but had no detailed knowledge of the subjects. Overall, AC was diagnosed in 283 (8%) women, but in only 54 of the men (1.7%). In the women, the prevalence of AC increased from 2.0% at age 45-49 years to 17.1% at the age of 70-74 years, while in men it was 0 and 8.3%, respectively. In women, multivariate analysis of risk factors showed AC to be positively related to systolic and negatively related to diastolic blood pressure, indicating a potential relation to pulse pressure. Furthermore, AC was independently associated with age, drug treatment for hypertension, nonfasting blood sugar, use of antidiabetic drugs, total serum cholesterol levels, and the amount of smoking. Too few men had AC for multivariate assessment of risk factors. In addition, in women AC was also related to a previous myocardial infarction (p < 0.05), mortality from coronary artery disease (p < 0.01), and the presence of intermittent claudication (p < 0.01). In men, however, AC was related only to total mortality (p < 0.05). Thus, these data show AC to be more prevalent in women, independently associated with recognized atherosclerotic risk factors, and a potential marker for coronary and peripheral artery disease.