Conjoined twins are born when a single fertilized egg partially splits into two fetuses. A hypothetical case of infant conjoined twins from Angel Mounds, a Middle Mississippian site (A.D. 1050–1400) on the Ohio River near Evansville, Indiana, was discovered in 1941. Morphological analysis does not rule out the field interpretation of this double burial as twins. Ancient mitochondrial DNA recovered from both infants demonstrates that they were not maternal relatives, and hence that they cannot have been conjoined twins. Am J Phys Anthropol, 2011. © 2011 Wiley-Liss, Inc.