The Mental Capacity Act 2005 (MCA) was fully implemented in October 2007 within England and Wales as a framework for making decisions about incapacitated persons' care and treatment generally not amounting to a deprivation of their liberty (although such could be authorised under its powers by the new Court of Protection). From a planned date of April 2009, the MCA is to be enlarged by the provisions of the Mental Health Act 2007 (MHA 2007) to encompass deprivation of liberty, with the addition of a new framework of Deprivation of Liberty Safeguards (DOLS). The MHA 2007 also revised significant aspects of the Mental Health Act 1983 (MHA), which were implemented in November 2008. The interface between the MCA, as amended to include DOLS, and the revised MHA is complex and potentially ambiguous. This paper describes in detail some issues that may arise at the interface of the two acts, and seeks to inform professionals involved in the use of these legal frameworks of the resulting complexity.