The concept of moral distress comes from nursing ethics, and was initially defined as ‘…when one knows the right thing to do, but institutional constraints make it nearly impossible to pursue the right course of action’. There is a large body of literature associated with moral distress, yet multiple definitions now exist, significantly limiting its usefulness. We undertook a systematic review of the argument-based bioethics literature on this topic as the basis for a critical appraisal, identifying 55 papers for analysis. (...) We found that moral distress is most frequently framed around individual experiences of distress in relation to local practices and constraints, and understood in terms of power relations and workplace hierarchies. This understanding is directly derived from, and often still seen as specific to, nursing. Frequently the perspective of the morally distressed individual is privileged. Understandings of moral distress have evolved towards an ‘occupational health approach’, with the assumption that moral distress should be measured and prevented. Counter-perspectives were identified, highlighting conceptual problems. Based on our review, we propose a redefinition of moral distress: ‘Ethical unease or disquiet resulting from a situation where a clinician believes they have contributed to avoidable patient or community harm through their involvement in an action, inaction or decision that conflicts with their own values’. This definition is specific enough for research use, anchored in clinicians’ professional responsibilities and concerns about harms to patients, framed relationally rather than hierarchically, and amenable to multiple perspectives on any given morally distressing situation. (shrink)