The purpose of this investigation was two-fold, first, to determine the incidence of amniotic sheets in our obstetric population; and, second, to elucidate the maternal and fetal complications associated with this particular finding. In this retrospective study, we searched the computerized records of the ultrasound department for the presence of amniotic sheets in singleton pregnancies from 1 March 1991 to 17 September 1993. Sonographic criteria for an amniotic sheet included the findings that (1) a reflective membrane attached to the placenta at one end or the other, with measurable thickness, was identified traversing the amniotic fluid; and (2) the fetus was not attached to the membrane, and fetal ability to move without restriction was ascertained. An amniotic sheet was identified in 79 of 17,553 examinations (0.45%) performed between 12 and 28 weeks' gestation. Two subsets of amniotic sheets were identified: perpendicular and not perpendicular. The sheets in the first subset were orientated perpendicular to the placental surface and were more likely to be associated with an abnormal presentation at delivery (p < 0.001) and a history of pelvic inflammatory disease, but not with a history of prior Cesarean section, or previous dilatation and curettage. The second subset of amniotic sheets were non-perpendicular, either oblique or parallel, in orientation to the placental surface and were associated with fewer maternal complications. Of the study group, 40.7% had a history of vaginal bleeding. The incidence of vaginal bleeding was not significantly different between those patients with perpendicular or those with non-perpendicular amniotic sheets. We conclude that perpendicular, in contrast to non-perpendicular, amniotic sheets are more commonly associated with breech presentation at term and a past history of pelvic inflammatory disease.