Background: Jargon aphasia is one of the most intractable forms of aphasia with limited recommendation on amelioration of associated naming difficulties and neologisms. The few naming therapy studies that exist in jargon aphasia have utilized either semantic or phonological approaches, but the results have been equivocal. Moreover, the effect of therapy on the characteristics of neologisms is less explored. Aims: This study investigates the effectiveness of a phonological naming therapy (i.e. phonological component analysis-PCA) on picture-naming abilities and on quantitative and qualitative changes in neologisms for an individual with jargon aphasia (FF). Methods & Procedures: FF showed evidence of jargon aphasia with severe naming difficulties and produced a very high proportion of neologisms. A single-subject multiple probe design across behaviours was employed to evaluate the effects of PCA therapy on the accuracy for three sets of words. In therapy, a phonological components analysis chart was used to identify five phonological components (i.e. rhymes, first sound, first sound associate, final sound and number of syllables) for each target word. Generalization effects-change in per cent accuracy and error pattern-were examined comparing pre- and post-therapy responses on the Philadelphia Naming Test, and these responses were analysed to explore the characteristics of the neologisms. The quantitative change in neologisms was measured by change in the proportion of neologisms from pre- to post-therapy and the qualitative change was indexed by the phonological overlap between target and neologism. Outcomes & Results: As a consequence of PCA therapy, FF showed a significant improvement in his ability to name the treated items. His performance in maintenance and follow-up phases remained comparable with his performance during the therapy phases. Generalization to other naming tasks did not show a change in accuracy, but distinct differences in error pattern (an increase in proportion of real word responses and a decrease in proportion of neologisms) were observed. Notably, the decrease in neologisms occurred with a corresponding trend for increase in the phonological similarity between the neologisms and the targets. Conclusions & Implications: This study demonstrated the effectiveness of a phonological therapy for improving naming abilities and reducing the amount of neologisms in an individual with severe jargon aphasia. The positive outcome of this research is encouraging, as it provides evidence for effective therapies for jargon aphasia and also emphasizes that use of the quality and quantity of errors may provide a sensitive outcome measure to determine therapy effectiveness, in particular for client groups who are difficult to treat.