Psychiatric intensive care units (PICUs) were first developed in the UK in the early 1970s and have become an integral part of inpatient services. This paper reviews all aspects of PICU provision from its origins to the most recent studies of intensive care treatment and philosophy. A search of CINAHL, MEDLINE and British Nursing Index databases revealed ample research and discussion papers from the past 30 years to permit a thorough review of the available literature. This divides roughly into discussion and descriptive research on topics related to: (a) the infrastructure of PICUs, including bed numbers, staffing levels, admission criteria and aspects of the physical environment; and (b) the treatment provided to patients on the PICU, both pharmacological and psychosocial, plus a limited amount of evaluative research on the efficacy of PICU care. This paper provides a summary and overview of these issues based upon currently available literature. It concludes that there is strong evidence for wide variation in the provision and nature of PICU care, reflecting idiosyncratic and localized development of services. Moreover, there is an almost complete lack of evidence on the efficacy of PICU care for particular types of patients and problems, leaving a paucity of research upon which PICU infrastructure, policy and therapeutic approach can be based.