ABSTRACT: If the ultimate success of efforts to improve pregnancy outcome depends on assurance that prenatal care begins in the first trimester, it is important to identify potentially modifiable factors associated with the start of care as well as the groups in which it is most likely to be late. This topic was explored in a population-based study of low birthweight in 766 black women and 462 white women who gave birth in Alameda County, California, in 1987. Variables related to insurance coverage and financial status showed the greatest difference between early and late attenders at prenatal care in both groups. At virtually every level of almost every variable studied, black women were less likely than white women to begin prenatal care in the first trimester. The data suggested that some of the difference in the timing of prenatal care may be due to lack of awareness of, or failure to pay attention to, the signs of early pregnancy. We conclude that, although addressing problems of insurance coverage and financial status is critical to the solution of the problem of late initiation of prenatal care, as financing difficulties are solved, attention should be paid to women's internal factors such as depression and denial as modifiers of the earliness of seeking prenatal care.