We prospectively identified 12 patients who had a shelf at the margin of the placenta consistent with the diagnosis of circumvallate placenta. Ten patients were followed to delivery and three placentas were sent for pathologic analysis. Circumvallate placenta was diagnosed by gross inspection in all three but was confirmed by microscopic analysis in only two. One of these patients had placental abruption and cesarean delivery for fetal distress at 27 weeks. Circumvallate placenta is another cause of uterine band, sheet, or shelf. The finding can be associated with a normal obstetric outcome but may predispose to placental complications.