People with jargon aphasia have severely disordered and incomprehensible speech that may be resistant to therapeutic intervention. In this study, we treated written output and examined whether it assisted communication for these clients. In stage one of the study, anagram sorting, delayed copying and lexical decision tasks were used to investigate the residual knowledge of written words in a group of ten people with jargon aphasia. Evidence of the presence of orthographic knowledge was taken as an indication that writing might be a useful focus for therapy. This hypothesis was explored in stage two with six clients. A personally useful vocabulary was selected for each, and copying, word completion and written picture-naming tasks were used in therapy to improve written production of these words. The clients made progress in written naming. However, they showed little change on a 'message' assessment that tested their ability to use the written words to convey messages. Stage three targeted communicative writing. Here, three of the clients received 'message therapy', which encouraged them to relate treated words to functional messages and to communicate them to a partner. The clients improved on the message assessment and observation of their communication and reports from relatives suggested that they made functional use of writing in a range of communication settings.