The authors' aim was to determine reference values and predictors for carotid intima-media thickness (CIMT) in the Bogalusa Heart Study. Carotid ultrasound images from 1203 young adults (mean age 36 years; 30% black, 43% male) were reviewed. Age-, sex-, and race-specific CIMT percentiles were estimated using multivariable regression. Nomograms of CIMT quartiles for persons aged 25 to 40 years are provided in 5-year increments. CIMT was thickest in the carotid bulb and increased linearly with age, most rapidly in the bulb. With age, composite CIMT increased most slowly in white women and more rapidly in white men and black women. Systolic blood pressure (P<.001) was the strongest predictor of composite CIMT. Male sex, total to high-density lipoprotein cholesterol ratio, and age independently predicted CIMT in all segments. This report may be used to help plan epidemiologic investigations and clinical trials investigating atherosclerosis and its changes with interventions.