In England in the early twentieth century, mental observation wards in workhouses developed as a parallel service to the asylums for emergency mental health admissions under the 1890 Lunacy Act, particularly in urban areas and especially London on account of local policy. The purpose of the wards was initial patient assessment and early discharge or certification, and there was controversy between their medical supporters and the Board of Control about any extension of their remit which might usurp the role of the mental hospitals. Their significance declined with changing policy in the NHS era, as more emergency admissions went to mental hospitals, and local treatment units emerged. This article explores the history of these services in the context of the changing legal and policy frameworks.