There are two reported cases in which courts have been asked to declare lawful surgery to separate conjoined twins where it is known that one twin will die during the procedure. Although judges granted the declaration sought, the two written decisions one from the common law jurisdiction of England and Wales, the other from a code jurisdiction in Queensland, Australia are problematic. This paper argues that neither of these cases provides a principled or certain basis for exculpating doctors in a future conjoined twin case, particularly if this case does not involve infant conjoined twins, one of whom is dying or is severely disabled.