The hospital opened on the 14th June, 1841 and admitted 299 patients that had all be examined by Alexander Morison, the visiting physician to Springfield, and taken out of various private madhouses around Surrey. The committee had not realised the demand that the Asylum would receive and in 1849 two further wings to the north of the building were opened, they had space for a further 400 patients, this cost the hospital a further £35,000.
Further additions were made to the buildings in the ever losing battle against increasing patient numbers, with two further wings being added to the south of the site in 1874.
To combat the problems with infectious diseases spreading through the hospital a cottage hospital was opened in 1872. The chapel was moved from within the main building to a purpose built chapel in 1880, in accordance with the Lunacy Commissions wishes. In 1885 a water tower was constructed to attempt to solve the water supply problems that were being experience from the two onsite wells, this was demolished in 1976.
The most ambitious extension to the site was construction of the Annex for Idiot Children whose purpose was to remove all the mentally handicapped patients, especially children, from the main wards within the hospital, this was opened on the 15th October, 1897.
Under the Mental Treatment Act of 1930 the annex was converted to house voluntary patients, it is now the admission block. This idea was strongly advocated by the current superintendent, Hugh Gardiner Hill and one of the committee members, John Langdon Down. The final extension, bar the current upgrades and extensions, was in 1931 when the infirmary block was opened.