"Mercy" holds a well-established place in the discourse on assisted death (AD), with mercy rhetoric used by both proponents and opponents of AD alike. In this paper, I interrogate the relationship between mercy, mercy killing and AD. Appeals to mercy introduce an ambiguity that carries implications for the enduring debate about healthcare professionals' participation in this controversial practice. The term "mercy killing" is used at different times to mean all of the following: killings that are acts of punitive leniency, killings motivated by pity, killings motivated by compassion, and acts of voluntary, involuntary and nonvoluntary euthanasia. I argue that killings that are acts of punitive leniency "track" a conceptually useful understanding of mercy and, by extension, mercy killing. However, if mercy is understood in this way, then "mercy killing" is a problematic way of characterizing physician-AD. While reference to mercy killing has been weeded out of AD legislation over time, the same cannot be said of public discourse, where the debate about physicians' character-and the locus of power with respect to who gets to decide when a life can rightly be ended-continues.