This paper uses discourse analysis techniques to analyze communication breakdown in the conversation of a youth with autism spectrum disorder (ASD). In demonstrating how discourse analysis can reveal unexpected and ordinarily unperceived meanings in unorthodox forms of expression in ways that are clinically relevant, this text analysis uncovers and examines not only ambiguities and conversational breakdown, but also unexpected coherence, in a discourse that appears to be incomprehensible. Beginning with a brief account of ASD, the paper goes on to present the linguistic framework for analysis, phasal analysis (Asp and de Villiers 2010; Gregory 1985a; Malcolm 2010), a contextually based model for the description of English discourse. Specifically, the approach is used for an analysis of prosodic, grammatical and discourse features. Analysis reveals meaningful linguistic patterning that indicates conversational participation, engagement and coherence not previously supposed, with important social and clinical implications.