A comparison of couples with and without psychopathology indicated that the couples in which one or both partners had a substance abuse disorder (SUD) were less warm and more hostile toward one another than couples with no psychopathology. Consistent with this finding, couples in the SUD group also engaged in higher rates of complex communications, mixing hostility and warmth. This does not mean that couples with no psychopathology resolved conflicts without hostility; however, the findings suggest that heightened levels of hostility may be a useful marker for identifying dysfunctional adolescent romantic relationships in which one or both partners have a substance use disorder or other types of psychopathology. No group differences were observed in assertiveness, control, submission, or autonomy-taking behavior, which suggests that level of interdependence or enmeshment may not be a good indicator of interpersonal dysfunction in adolescent couples. The discrepancy between self-appraisal and observed behavior noted among the sample of adolescents emphasizes the importance of using observational techniques, which may provide a more accurate and complete assessment of relationship quality. Two groups of adolescent couples were recruited to participate in the study. One was classified as a high-risk group (n=18 couples), in which one or both partners had a SUD. The other group was classified as low risk (n=12 couples), since neither partner had a history of psychopathology. Self-report and observational data on couples’ relationships were collected from both groups. Couples’ observed conflict interactions were coded, using the structural analysis of social behavior (Florsheim and Benjamin, 2001). 2 tables, 1 figure, and 62 references