Serum lipids and lipoprotein cholesterol fractions were examined in a newborn cohort that was followed from birth to 7 years of age. Although white and female infants had higher cord blood levels of high-density lipoprotein cholesterol (HDL-C) than did black and male infants, respectively, these differences did not persist throughout early childhood. Mean levels of all serum lipids and lipoproteins increased greatly in the first 6 months of life, and by 2 years of age, levels approached those seen in adolescents. Infants consuming cow's milk had higher 6-month levels of serum total cholesterol and low-density lipoprotein cholesterol than did formula-fed infants. However, milk source in infancy did not significantly influence total cholesterol or low-density lipoprotein cholesterol levels at age 7 years. Serum lipid and lipoprotein levels at age 7 years were associated with previously measured levels as early as 6 months of age, and infants with unfavorable levels were likely to have similar adverse levels at 7 years of age. In addition, increases in obesity between 6 months and 7 years of age were positively associated with increases in levels of serum triglycerides. These results suggest that certain persons at increased risk for cardiovascular disease can be identified in infancy.