Whilst current mental health care provision has made a substantial move towards empowering its users it retains a paternalistic approach with legislation such as 'supervised discharge'. This apparent paradox creates potential dilemmas for the mental health nurse and suggests there is a need for critical analysis of the justification for paternalism within mental health care. This paper discusses the conflict between the ethical principles of autonomy and beneficence which paternalism invokes. On reviewing the ethical theories of deontology and utilitarianism it appears that a prerequisite for autonomy is rationality, the absence of which provides justification of 'weak' paternalism. However, this paper contends that the assessment of rationality has the potential to be subjective and value laden. The use of competency tests can also be problematic by masking the essential ethical dilemma that is intrinsic to such assessment. A case study is used to illustrate the strengths and weaknesses of the competing arguments. This leads to the conclusion that whilst there may be some situations when the use of paternalism can be justified in mental health care, it should be exercised with caution. When there is disagreement between nurse and patient on what is considered to be in the patient's best interests, it should not be assumed that the patient is wrong or irrational.