The Adult Psychiatric Morbidity Survey (APMS) 2007 is the third survey of psychiatric morbidity among adults living in private households. It was carried out by the National Centre for Social Research (NatCen) in collaboration with the University of Leicester, and was commissioned by The NHS Information Centre for health and social care. The main aim of the 2007 survey was to collect data on mental health among adults aged 16 and over living in private households in England. It is the primary source of information on the prevalence of both treated and untreated psychiatric disorders and their associations: data which cannot be obtained from other sources. As with the surveys of adult psychiatric morbidity conducted in 1993 and 2000, a two-phase approach was used. The first phase interviews included structured assessments serving diagnostic criteria and screening instruments for a range of mental disorders, as well as questions on topics such as general health, service use, risk factors and demographics. The second phase interviews were carried out by clinically trained research interviewers. A subsample of phase one respondents were invited to take part in a second phase interview. The assessment of conditions such as psychosis and personality disorder required a more flexible interview than was possible at the first phase, and the use of clinical judgement in ascertaining a diagnosis.