We theorized that relational uncertainty fosters a pessimism bias that leads spouses to process messages negatively. We conducted a study in which 125 couples engaged in videotaped conversations. Although participants reported modest levels of relational uncertainty, our results were consistent with our predictions. Relational uncertainty predicted individuals’ judgments of the affiliation, dominance, and involvement of their partner's messages (H1, H2), but it was not associated with the perceptions of outside observers (RQ1). Relational uncertainty was positively associated with spouses’ appraisals of the self threat and relationship threat of conversation (H3, H4) and their feelings of negative emotion (H5). Hence, spouses experiencing mild relational uncertainty may be reactive to conversations that seem ordinary to outside observers.