Objective: To determine whether racial differences in risk of low birth weight infants among black and white parents can be attributed to differences in demographic, behavioral, medical, and socioeconomic factors.Methods: We analyzed 203,815 singleton births from the 1992 California birth certificate data set for the risk of very low birth weight (500 -1499 g) and moderately low birth weight (1500 -2499 g) infants. Additional study variables included maternal (race, age, education, marital status, parity, obstetric history, tobacco use, medical complications, medical insurance, and use of prenatal care), paternal (race, age, and education), infant (gestational age and gender), and community (median household income from the 1990 US Census) characteristics.Results: For both very low and moderately low birth weight infants, the unadjusted risk associated with parental race showed a gradient of risk, from highest to lowest, for black mother/black father, black mother/white father, white mother/black father, and white mother/white father parents. After adjusting for other risk factors, the odds ratio associated with black mother/black father parents was reduced from 3.37 to 1.73 for very low birth weight infants and from 2.51 to 1.60 for moderately low birth weight infants, but both remained elevated. Interracial parents no longer had an elevated risk of very low birth weight infants and white mother/black father parents no longer had an elevated risk of moderately low birth weight, compared with white parents.Conclusion: After controlling for parental, infant, and community factors, most but not all of the increased risk of low birth weight infants associated with black parental race was explained. (Obstet Gynecol 1998;92:814 -22. © 1998 by The American College of Obstetricians and Gynecologists.)Low birth weight infants (weight less than 2500 g) have an increased risk of morbidity and mortality during infancy and childhood. 1 In the United States, black women consistently have higher rates of low birth weight infants and infant mortality than do white women. 2 From 1975 through the early 1990s, the rates of low birth weight infants for blacks were more than double the rates for whites. 3,4 The persistence of differences in perinatal outcomes between blacks and whites is a major public health and policy issue and has spurred intensified efforts to identify causal factors for adverse health outcomes. 5 Researchers of several studies have tried to identify the attributes responsible for higher rates of low birth weight in black women. 6 -11 Even after controlling for known risk factors, such as age, education, smoking, gestational age, use of prenatal care, and medical complications, racial differences in rates of low birth weight have persisted. These unexplained racial differences in low birth weight have led to speculation that blacks are predisposed to lower birth weight infants, 12 a theory that has not been supported by recent studies. [13][14][15] To improve perinatal outcomes in the United States, it is extr...