Aphasia is an acquired language disorder resulting from trauma or injury to language areas of the brain. Despite extensive research on the impact of aphasia on traditional forms of communication, little is known about the impact of aphasia on computer-mediated communication CMC). In this study we asked whether the well-documented language deficits associated with aphasia can be detected in online writing of people with aphasia. We analyzed 150 messages 14,754 wordsposted to an online aphasia support forum, by six people with aphasia and by four controls. Significant linguistic differences between people with aphasia and controls were detected, suggesting five putative linguistic HCI markers for aphasia. These findings suggest that interdisciplinary research on communication disorders and CMC has both applied and theoretical implications.