A case-control study of the epidemiology of preterm delivery was undertaken at Yale-New Haven Hospital in Connecticut during 1977. The study population consisted of 175 mothers of singleton preterm infants and 313 mothers of singleton term infants. Significant risk factors of a preterm delivery included low socioeconomic status; low pregravid weight; inadequate weight gain during the pregnancy; a previous preterm delivery; a history of infertility problems; an induced abortion terminating the previous pregnancy; vaginal spotting or light bleeding during the pregnancy; antepartum hemorrhage and abnormal placental implantation; lack of leisure-time physical activities during the pregnancy; alcohol consumption prior to the third trimester of pregnancy; and negative attitudinal expression toward the pregnancy.