OBJECTIVES: The purpose of this study was to expand the search for risk factors for low birthweight and to find new explanations for the ethnic-group disparities in birth outcomes. METHODS: The subjects were 1150 pregnant women from six ethnic groups (African American, Chinese, Dominican, Puerto Rican, Mexican, and White) who received prenatal care at clinics in New York and Chicago between December 1987 and December 1989. Two interviews were conducted during the second and third trimesters of pregnancy. RESULTS: The study, after controlling for poverty and other birthweight correlates, showed that living in public housing and believing that chance plays a major role in determining one's health status were negatively associated with birthweight. Having a stable residence was positively related to birthweight. Material hardship, social adversity, perceived racial discrimination, physical abuse, anxiety, and depression were not associated with birthweight. CONCLUSIONS: The negative role of an impoverished living environment and feelings of helplessness, as well as the positive role of having a stable form of social support, suggest new directions for research on the causes of low birthweight and the ethnic disparities in US birth outcomes.