This investigation of student perceptions of mediated presence in an online college class yielded two key findings. First, perceptions of the instructor's mediated presence were significantly higher than perceptions of the other students' presence. Second, students identified a set of communication behaviors that influenced their perceptions of whether other participants in the class were "real" or present: frequency of interaction, responsiveness, use of non-verbal communication channels, and participants' tone or communication style. Theoretical and pedagogical implications of these findings and directions for future research are discussed.