The Coronary Artery Risk Development in Young Adults (CARDIA) study completed baseline dietary assessment, measurement of body mass index, and lipid and lipoprotein analyses on 5,111 participants. CARDIA includes black and white men and women between 18 and 30 years of age at baseline (1985-1986), recruited in Birmingham, Alabama, Chicago, Illinois, Minneapolis, Minnesota, and Oakland, California. Diet was assessed by a detailed interviewer-administered diet history that measured the usual eating pattern over the past month. Possible sex, race, age, and educational differences in diet, body size, and lipids-lipoproteins were explored. Nutrient analyses indicate that the Keys score, a measure of dietary fat composition, is significantly correlated with plasma cholesterol in older (aged 25-30 years) white men (r = 0.12, p less than 0.01) and older white women (r = 0.12, p less than 0.001). In multiple linear regression analyses, body mass index was positively and significantly associated with total cholesterol and low density lipoprotein cholesterol and inversely associated with high density lipoprotein cholesterol across all race-sex groups. The Keys score was significantly associated with total cholesterol and low density lipoprotein cholesterol in white men and women. Education was associated with high density lipoprotein cholesterol in black and white women and white men. In these young adults, dietary fat intake and body mass index were related to blood lipids in certain subgroups. In black and white men and black women, blood cholesterol increased with age across race-sex groups independently of these covariates. In view of the many factors affecting plasma cholesterol and the limitations of the dietary history method, these cross-sectional data are useful in characterizing diet and lipid differences. There appears to be general disparity between recommended dietary intake of total fat, saturated fat, and other nutrients and actual dietary intake in young adults, regardless of age and educational level.