Objective: To document the relation between stillbirth and various demographic, obstetric, and medical risk factors.Methods: We analyzed the risk factors and medical origins of 403 stillbirths. The population studied included 34,350 births occurring during the March of Dimes Preterm Birth Prevention Trial. All births occurring in five perinatal centers from 1982–1986 were included in the analysis. Stillbirth was defined as those infants born at 20 weeks' gestation or later whose Apgar score was 0 at 1 and 5 minutes.Results: Stillbirth occurred in 1.2% of all births. Fifty-one percent occurred before 28 weeks and only 18% were at term. Blacks had a greater risk of stillbirth when compared to other women. Prior preterm delivery yielded nearly a twofold increase in the risk of stillbirth. Preeclampsia, chronic hypertension, and class A or class B-R diabetes were not associated with an increased risk of stillbirth. Other medical factors (hemoglobinopathies, Rh sensitization) resulted in a greater than sixfold increase in the rate of stillbirth, and congenital anomalies resulted in a fivefold increase. Abruption was associated with a 12-fold increase in the risk of stillbirth; nearly 14% of all stillbirths were associated with abruption.Conclusion: Eighty-two percent of all stillbirths occurred before term, and more than 50% occurred before 28 weeks. The majority of stillbirths were not explained by medical complications, but instead were often associated with other risk factors related to preterm birth. Further investigations are needed to understand the complex etiology of stillbirth.