St Mark's colo-rectal hospital celebrated its 150th anniversary in 1985. It is the only colo-rectal hospital to survive in Britain and thus is unique. It is also a particularly distinguished example from a class of hospitals that developed in the nineteenth century in London and elsewhere to combat specific diseases, or to specialise in a field of work. This study traces the development of the hospital in the context of the rapidly growing metropolis and the changing medical profession.