The lengthy Byzantine romance Persiles y Sigismunda, which Cervantes completed only days before his death in 1616, has conventionally been considered a relatively pure example of romance fiction. This study of genre in the Persiles questions that view by analysing the novelistic or realist aspects of the work. An extensive comparison with examples of Byzantine romance from its Greek origins to its Renaissance evolution highlights the degree to which Cervantes departs from the established canon, notably in the characterisation of the heroine and the significance of the protagonists' wedding, where Cervantes upsets the reader's expectations of a conventional happy ending by consistent use of an ironic mode typical of the work. Multidimensional characters, contrasting perspectives and ironic manipulations produce a kind of 'generic hybridisation' which exposes the fallacies of this type of fiction. MARIA ALBERTA SACCHETTI holds a doctorate from University College London.