Neuroticism has repeatedly been shown to be a predictor of relationship dissatisfaction in couples. The aim of the current research was to uncover the underlying cognitive processes of this robust effect. We focused on anxiety as one aspect of neuroticism that is associated with different kinds of cognitive biases. On the basis of the assumption that biased information processing will also affect specific interpersonal contexts such as romantic relationships, it was expected that the tendency to interpret ambiguous partner and relationship scenarios in a rather negative way would work as a potential mediator. In Study 1, parallel forms of a new measure to capture the relationship-specific interpretation bias (RIB) were developed (N = 182). In Study 2, the proposed meditational role of the RIB was investigated in a dyadic sample of 210 couples. Dyadic analysis using the Actor–Partner Interdependence Mediation Model showed mediation of the interpretation bias even when the general interpretation bias and attachment styles were controlled. Results support the assumption that biased relationship-specific interpretations are one important mechanism for how neuroticism exerts its negative influence on relationship satisfaction. We conclude that personality-congruent cognitive processing may not only have individual consequences but also affect overall couple functioning. Copyright © 2013 John Wiley & Sons, Ltd.