Researchers have debated the benefits of having accurate knowledge about a close other's personality. However, the existing research has examined personality knowledge solely in terms of traits. Although trait knowledge may be useful during relationship selection, we hypothesize that once a relationship becomes established, accurate personality knowledge about the other person's if-then profiles--the person's characteristic patterns of responses to situations--may be particularly beneficial. We conducted the first study of if-then accuracy in close relationships. To do so, we developed the If-Then Trigger Profile Questionnaire, which consists of 72 descriptions of potentially bothersome interpersonal behaviors. Participants in this study selected a friend to participate with them. Both friends then rated how much each behavior tended to trigger a negative emotional reaction in themselves personally and how much each behavior might trigger a negative emotional reaction in their friend. Findings demonstrated that accurate knowledge about a friend's if-then trigger profile is associated with reduced feelings of conflict and increased feelings of depth in the relationship.