Background Little is known about the current state of provision of child and adolescent mental health service in-patient units in the UK. Aims To describe the full number, distribution and key characteristics of child and adolescent psychiatric in-patient units in England and Wales. Method Following identification of units, data were collected by a postal general survey with telephone follow-up. Results Eighty units were identified; these provided 900 beds, of which 244 (27%) were managed by the independent sector. Units are unevenly distributed, with a concentration of beds in London and the south-east of England. The independent sector, which manages a high proportion of specialist services and eating disorder units in particular, accentuates this uneven distribution. Nearly two-thirds of units reported that they would not accept emergency admissions. Conclusions A national approach is needed to the planning and commissioning of this specialist service.