Purpose. This paper highlights aspects of the current state of research and thinking about ethical issues in relation to Brain Computer Interface (BCI) and Brain-Neuronal Computer Interfaces (BNCI) research through the experience of one particular project, BrainAble, which is exploring and developing the potential of these technologies to enable people with complex disabilities to control a computer. It describes how ethical practice has been developed both within the multidisciplinary research team and with participants.Results. The paper presents findings from the project in which participants shared their views of the project prototypes, of the potential of BCI/BNCI systems as an assistive technology, and of their other possible applications. This draws attention to the importance of ethical practice in projects where high expectations of technologies, and representations of 'ideal types' of disabled users may reinforce stereotypes or drown out participant 'voices'. Conclusions. Ethical frameworks for research and development in emergent areas such as BCI/BNCI systems should be based on broad notions of a 'duty of care' while being sufficiently flexible to allow researchers to adapt project procedures according to participant needs. They need to be frequently revisited, not only in the light of experience, but also to make sure that they reflect new research findings and ever more complex and powerful technologies. Implications for Rehabilitation• BCI/BNCI systems are not similar to existing switch-controlled or eye gaze systems. Users and those supporting them need to have their expectations carefully managed.• BCI/BNCI are emergent technologies and side effects of long term use are not well understood: this demands an ongoing concern to ensure duty of care and maintenance of a 'watching brief' regarding ethical issues.• Practitioners need to be particularly careful when introducing BCI/BNCI systems to be sensitive to the meanings that are attached to them and how they may convey prognosis.

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