The Mental Capacity Act (2005) has been in force since 2007. It applies to people who lack the mental capacity to make decisions for themselves. The Act aims to safeguard the principle that people, when they have capacity to do so, should be able to make their own decisions about the medical and social care they receive. This emphasis on patient autonomy has led to concerns being raised in areas where traditionally a more paternalistic approach to care has been the norm and where the application of the Mental Capacity Act has been novel and has led to confusion. A good example is when people with a history of self-harming behaviour present themselves at accident and emergency departments. In June 2010, the Mental Health Foundation released figures suggesting that 52% of health and social care professionals were misinterpreting the Mental Capacity Act by not assuming that patients had capacity before conducting the assessments. Indeed, since the legislation was brought in there has been little debate on how well it is working in practice, from the points of view of both medical and social care staff and patients. This POSTNote will explore the current interpretation of the Mental Capacity Act by health professionals, and highlight the policy options for amendments both to the legislation and to relevant codes of practice.