ABSTRACT If a doctor kills a severely handicapped infant, he commits an act of murder; if he deliberately allows such an infant to die, he is said to engage in the proper practice of medicine. This is the view that emerged at the recent trial of Dr Leonard Arthur over the death of the infant John Pearson. However, the distinction between murder on the one hand and what are regarded as permissible lettings die on the other rests on the Moral (...) Difference Myth, according to which deliberate lettings die in the practice of medicine are not instances of the intentional causation of death. I argue that a doctor who refrains from preventing a handicapped infant's death, causes that infant's death and does so intentionally. He commits an act of murder. But, I suggest, not all instances of the intentional causation of death are morally wrong. To the extent that they are not, killing rather than letting die will often be the preferable option because more economical of suffering. Hence what is required is the abolition of the Moral Difference Myth and legislation to the effect that those doctors who justifiably cause a patient's death—whether by an action or by an omission—commit no offence. (shrink)