This study examined the association between language style matching (LSM), subjective perceptions of interaction quality (perceived responsiveness and affect), and partner behavior in two communication contexts: conflict and social support. Romantic couples (N = 91) engaged in a video-recorded discussion of either a relationship stressor or one partner’s personal stressor (a social support discussion). LSM was associated with unique outcomes in each communication setting. Higher LSM was associated with lower subjective perceptions of responsiveness and less positive emotion for partners discussing relationship stressors but more positive emotion for partners in social support discussions. Furthermore, higher LSM was associated with more critical and negative interpersonal behavior and less responsive and caring behavior during discussions of relationship stressors but was unrelated to behavior in support discussions. Findings suggest that LSM does not uniformly signal interpersonal rapport (as often assumed) and may instead amplify the positive or negative tone of an interaction.