Advances in kidney transplantation over the past six decades have been impressive, but have not eliminated the significant variability in outcome related to donor organ quality. Organ shortage means that, in addition to ‘standard’ deceased donor kidneys (SD), ‘non-standard donor’ (NSD), ‘expanded criteria donor’, or ‘marginal’ kidneys, which fail to meet standard criteria and are often associated with less good outcomes, are now being transplanted into selected recipients as a means of increasing the donor pool. A similar, but less-documented, practice has developed in living donation. This article outlines the clinical rationale and ethical argument underpinning the use of such donor kidneys and examines their legal status in the UK, which we claim remains largely undefined and untested. While it is probable that the general principles governing medico-legal consent and liability also apply to organ donation, the special circumstances of donation, notably the inadequate supply of donors and the emphasis on a ‘gift relationship’, make it difficult to know how far existing medico-legal precedents can or should apply. The non-standard status of deceased donor organs creates potential problems for the validity of ‘appropriate consent’ to donation required by statute. It may also be relevant to the use of interventions intended to optimise deceased donor organ quality. Furthermore, the SD/NSD distinction in clinical practice may produce unexpected legal effects. For example, the recent UK Regulations 2012, which bring into force the EU Directive on standards of quality and safety of human organs intended for transplantation, could produce a negative legal restraint on the use of NSD kidneys. There is an urgent need for clarification of the effect of using NSDs in areas such as recipient and donor consent, liability for negligence, and the law of product liability. Some argue that the need for non-standard organs results from society's failure to compel the retrieval of all suitable standard organs from the deceased as a community resource. However, the Human Tissue Acts of 2004 and 2006 (Scotland), which govern organ donation and transplantation in the UK, expressly require individual consent or authorisation in the decision to donate. This emphasis on individual autonomy appears to chime with prevailing public opinion. However, the sense of medico-legal security gained by uncritical observance of the existing law and of directives published under its authority may be an obstacle to the development of a system which adequately meets the needs of recipients while safeguarding donor autonomy.