Application of informatics to mental health has the potential to benefit a disadvantaged yet important patient group. At the same time, difficult issues are raised with regard to data protection and ethics because many patients are not able to express informed and rational views, and this increases their vulnerability.

However, developments in this field are limited, and there is little literature. Generic data protection legislation and guidance assumes that data subjects are mentally competent adults. This paper distils key ethical issues and principles in mental health informatics, and describes a process which has initiated the identification of “reasonable” practice.