Mogden Isolation Hospital, Mogden Lane, Isleworth was opened in 1898 by the Borough of Richmond (Surrey) and Heston and Isleworth Urban District Joint Isolation Hospital Committee for the treatment of patients suffering from scarlet fever, diphtheria, enteric fever, measles, and other infectious diseases. It partially replaced Dockwell Isolation Hospital, situated near Cranford, but in the parish of Heston, which was retained for the treatment of smallpox cases. In between smallpox epidemics the hospital stood empty for several years at a time. When necessary, staff were allocated to the hospital from Mogden.
By the late 1920s the Joint Isolation Hospital Committee had to decide whether to replace the buildings at Dockwell Hospital or to make alternative arrangements for the treatment of smallpox patients. The "old building" next to the Administration Block was sold by auction in 1921. In 1926 Richmond Council reached agreement with the Surrey Smallpox Hospital Committee for the reception and treatment of smallpox patients from Richmond at Surrey Smallpox Hospital, Clandon. Though Dockwell Isolation Hospital was brought into use in 1928 to admit ten smallpox cases and in 1930 for the treatment of diphtheria patients, it had finally closed by 1935.
In that year the Joint Isolation Hospital Committee ceased to exist. On 1 April 1935 the South Middlesex and Richmond Joint Hospital Board took over control of Mogden, Twickenham and Hampton Isolation Hospitals. Hampton Isolation Hospital closed in July 1935. After a further reorganisation in September 1935, all acute cases except certain less common infections were admitted to Mogden Hospital. Twickenham Isolation Hospital was used only for a few enteric fever cases, some rarer infections, and "clean" scarlet fever cases. Twickenham Hospital closed in 1938 on the completion of substantial additional buildings at Mogden Hospital, which was renamed the South Middlesex Fever Hospital.
A report by visitors from King Edward's Hospital Fund for London in 1953 described the new South Middlesex Hospital "This was built between the wars, apparently regardless of cost, by a joint board consisting of the Boroughs of Richmond, Twickenham and Heston and Isleworth. There are four wards, each being separate single storey blocks, two in horse shoe form facing south containing 24 beds in cubicles. The other two are straight wards, one cubicled and the other open." An operating theatre was provided adjoining one of the horse shoe wards. The main kitchen "is enormous and could cook for 1,000. The nurses' home is large and magnificent, but lacks something in homeliness" (ref. A/KE/735/48). A laboratory and administrative block were also built in 1938 and work was set in hand to modernise the old wards.
On the outbreak of war in 1939, the large pavilion wards were taken over by the Emergency Medical Service. Extra beds were provided by the Ministry of Health making a total of 227 beds available for casualties. 96 beds in the two cubicle blocks remained in use for infectious diseases. Extra nursing, clerical and domestic staff were transferred from Westminster Hospital and other London hospitals. A team of medical staff from St George's Hospital and the West London Hospital took up residence at the South Middlesex Hospital. In October 1940 26 beds in Ward VII were set aside for the surgical treatment of gynaecological cases. This work was expanded in 1941, so that in 1942 a total of 302 gynaecological patients were admitted. For case notes for gynaecological cases transferred to the South Middlesex Hospital from Chelsea Hospital for Women 1940-1945 see H27/CW/B3/1-5. 1947 saw a substantial increase in admissions of patients suffering from infectious diseases caused by epidemics of measles and polio and the admission of patients from Acton.
In 1948 South Middlesex Hospital became part of the National Health Service as one of the South West Middlesex group of hospitals of the North West Metropolitan Regional Hospital Board. In 1953 the King's Fund visitors found that the hospital had 144 beds of which 83 were in use. "Two of the wards are used for fevers, one is closed and the fourth open ward is the surgical ward used by Dr Galloway from the West Middlesex Hospital" (ref. A/KE/735/48). In 1955 one of the smaller buildings was converted into an ophthalmic department with its own operating theatre to provide a regional ophthalmic unit. By 1973 the South Middlesex Hospital was described as mainly acute. On the reorganisation of the National Health Service in 1974 it was transferred to the Hounslow Health District of Ealing, Hammersmith and Hounslow Area Health Authority (Teaching). After 1982 it became the responsibility of Hounslow and Spelthorne Health Authority. The hospital closed around 1991.