Isherwood, who grew up in England, came to Berlin through his friend, Francis Turville-Petre, in 1929 and stayed with him at the Institute until 1930.
Hirschfeld evidently did not make any distinction between visitors and residents at his institute. In his book "Christopher and His Kind", Isherwood refers to Hirschfeld's "eye for a patient":
"Like the young man with the female breasts and everyone else who entered the domain of the Institute, Christopher had automatically become a museum specimen, subject to Hirschfeld's diagnosis and classification. Karl told him..., that Hirschfeld had classified him as 'infantile.' Christopher didn't object to this epithet; he interpreted it as 'boyish.'"
Isherwood, who, together with Francis Turville-Petre and Wystan Hugh Auden, stayed on in Berlin until 1933, left Germany subsequently. In 1946, he became an American citizen and worked as a literature professor. He was made famous by, amongst others, his book "Goodbye to Berlin" on which the musical "Cabaret" was based. He died in Santa Monica, California, in 1986.