Causal uncertainty (CU) refers to persistent doubts people have about their ability to understand causes of social events. Although such confusion about social dynamics should affect social exchanges, previous research has been limited to the realm of social cognition (i.e., computer-based studies exploring perceptions of hypothetical others). In three studies, we explored CU effects during real-time social interactions with unacquainted conversational partners. We found that high CU participants perceived their conversations and conversational partners more negatively than did low CU participants and that these negative social perceptions stemmed from an inability to sufficiently reduce their cognitive uncertainty. Copyright © 2012 John Wiley & Sons, Ltd.