The language of Brendan Behan’s The Quare Fellow (1954), a play set in an Irish prison, is examined stylistically. This is done under the headings of naming, usage of Hiberno-English, of prison jargon, and of Gaelic. These show evidence of categorisation under the conventional class structure of upper, middle, and lower. However, there are more complex divisions present through language. These are: prisoners’ pecking-order according to crime, prisoners using more Hiberno-English and also prison jargon than the authority figures, one warder who uses language patterns similar to the prisoners, and the use of Gaelic by two characters, one a warder and the other a prisoner, who along with the warder above, represent the moral core of the play. Keywords: Brendan Behan; The Quare Fellow; stylistics; class structure.