We integrate research on team functioning with that of self-awareness to advance the notion of self-awareness in teams as an important concept to consider when diagnosing team effectiveness. We argue that teams composed of individuals with greater levels of self-awareness will exhibit more effective team-level functioning and performance. This proposition was explored by examining the effects of self-other agreement with regard to individual-level contributions of teamwork behavior on three team-level functional outcomes (team coordination, conflict, cohesion) and team performance. Results from 515 teams (2,658 individuals) completing a high-fidelity team-based business simulation supported the effects of aggregate levels of self-awareness on team-level functioning and performance. Moreover, these effects were influential above and beyond individual contributions themselves, highlighting the unique value of team members’ self-awareness for understanding team functioning. Of the three functional outcomes, only team conflict mediated the effects of self-awareness in teams on subsequent team-level performance. Finally, results revealed that overrating among team members was a particularly problematic form of the lack of self-awareness in teams.