To assess whether carotid atherosclerosis measured by B-mode ultrasound is related to cardiovascular risk factors, 386 cases with carotid artery wall thickening and an equal number of controls free of arterial intima-media thickening were drawn from the cohort of the Atherosclerosis Risk in Communities (ARIC) Study examined in four communities in the United States between 1988 and 1990. Cases and controls were individually matched on sex, race, age group, study center, and date of examination. The mean values of total cholesterol, low density lipoprotein (LDL) cholesterol, total triglyceride, blood pressure, and pack-years of cigarette smoking were higher in cases than controls. Mean high density lipoprotein (HDL) cholesterol was lower in cases than controls. Case-control differences were all statistically significant. Multivariable-adjusted odds ratios point to differences of considerable magnitude in the risk of carotid atherosclerosis between groups defined by clinical and public health-oriented risk factor cut-points.