To investigate cardiovascular risk factors and carotid atherosclerosis, we related previously measured risk factors to carotid atherosclerosis as determined by duplex ultrasonography in the Framingham Study cohort. Risk factors measured prospectively on 1,116 cohort members, ages 66 to 93, were related to the severity of carotid atherosclerosis measured by carotid ultrasonography performed during biennial examination no. 20 (1988 to 1990). The degree of carotid atherosclerosis was expressed as a percent carotid stenosis and, for statistical analysis, subjects were divided into four groups according to percent carotid stenosis. The prevalence of significant carotid stenosis in the general population was low--7% in women and 9% in men. A multivariate logistic regression model showed that age, cigarette smoking, systolic blood pressure, and cholesterol were independently related to carotid atherosclerosis. Alcohol consumption was also significant in men, but not in women. In addition, our results indicate that both current and former smoking in both sexes was related to the degree of carotid atherosclerosis.