Since the 1980s, there has been an increasing acknowledgement of the importance of recognising the ethical dimension of clinical decision-making. Medical professional regulatory authorities in some countries now include ethical knowledge and practice in their required competencies for undergraduate and post graduate medical training. Educational interventions and clinical ethics support services have been developed to support and improve ethical decision making in clinical practice, but research evaluating the effectiveness of these interventions has been limited. We undertook a systematic review of the published literature on measures or models of evaluation used to assess the impact of interventions to improve ethical decision making in clinical care. We identified a range of measures to evaluate educational interventions, and one tool used to evaluate a clinical ethics support intervention. Most measures did not evaluate the key impact of interest, that is the quality of ethical decision making in real-world clinical practice. We describe the results of our review and reflect on the challenges of assessing ethical decision making in clinical practice that face both developers of educational and support interventions and the regulatory organisations that set and assess competency standards.