Parent–child relationships are hotbeds of emotion and play a key role in mental health. The present proof-of-concept study examined facial expressions of emotion during adolescent–parent interactions and links with internalizing mental health symptoms. Neutral, negative, and positive facial expressions were objectively measured in 28 parent–adolescent dyads during three 10-min dyadic interactions. Internalizing mental health symptoms were measured using anxiety and depressive symptom questionnaires. Data were analyzed using actor–partner interdependence modeling. Results revealed that higher levels of (a) adolescents’ neutral facial expressions as well as (b) parents’ negative facial expressions were associated with higher levels of adolescents’ mental health symptoms. Findings did not support a robust link between (c) positive expressions and mental health symptoms. Together, these results demonstrate the utility of facial expressions of emotion during parent–child interactions as behavioral correlates of adolescents’ internalizing mental health symptoms, highlight the need for replication with larger samples, and suggest directions for future research.