This retrospective study examined the effects of very prolonged membrane rupture of more than 1 week on the development of pulmonary hypoplasia and positional deformities in the infants of 100 consecutive women. A control group of infants who were matched for gestational age at delivery, sex, and time of delivery was identified. The results indicate that there was a statistically significant difference (p less than 0.001) in the occurrence of pulmonary hypoplasia and positional deformities. The greatest impact of prolonged membrane rupture on fetal development was seen in the patients in whom membrane rupture occurred prior to 26 weeks' gestation and the duration of rupture was more than 5 weeks.