The neuropsychological mechanisms underlying unawareness of speech/language deficits are unknown, but four possibilities have been suggested: impaired lexical-semantic representations associated with impaired speech comprehension, a failure of feedback, reduced attentional capacity, and psychological denial. We studied a patient who was unaware of his jargon aphasia despite only a mild auditory comprehension disturbance. Delaying auditory feedback altered his speech patterns. He recognized more of his errors in a recording of his voice than he did while speaking. He also recognized more errors in a recording of the examiner making errors than he did when listening to the recordings of his own speech. Based on these results, we suggest that none of the proposed mechanisms can exclusively account for this man′s performance and that each may contribute to his failure to detect and correct errors in speech production. © 1994.