Some patients with aphasia lack awareness of the language errors they make. We describe a man with undifferentiated jargon-aphasia and preserved auditory comprehension who was unaware of his speech production errors when he had to both speak and listen simultaneously. However, when listening to a recording of his speech, he could detect the speech errors he had made. We attribute this patient’s unawareness of his speech production errors to a reduced attentional capacity for simultaneous linguistic tasks. © 1995 American Academy of Neurology.