Sufferers of body integrity identity disorder (BIID) experience a severe, non-delusional mismatch between their physical body and their internalised bodily image. For some, healthy limb amputation is the only alleviation for their significant suffering. Those who achieved an amputation, either self-inflicted or via surgery, often describe the procedure as resulting in relief. However, in England, surgeons who provide ‘elective amputations’ could face prosecution for causing grievous bodily harm (GBH) under section 18 of the Offences Against the Persons Act 1861. Whether such a therapeutic intervention should be classified as GBH depends on the presence of harm, as, without harm, it is hard to argue that GBH has occurred. However, there is no agreed-upon definition of what constitutes harm. Such a definitional absence then begs the question, what is harm? It is this question which this article addresses, using the provision of healthy limb amputation in cases of BIID as an example. Drawing on metaphysics, this article will seek to clarify three separate contemporary models of harm: the counter-temporal, the counterfactual, and the non-comparative. Each model will be applied to the scenario of a surgeon carrying out a BIID-induced, therapeutic, healthy limb amputation, and in each, how harm may, or may not, be understood to have been caused will be explored. It concludes that an unexamined conception of harm is ill-equipped for employment in suspected cases of GBH when it is unclear whether harm has been caused and that a better-informed understanding of harm is required in cases where there is potential disagreement, be that in instances of BIID or a myriad of other borderline scenarios.