The Parent Behavior Change Intervention (PBC-I) was developed to target parent-adolescent conversations that promote adolescent health behavior change. We report on an open trial of the PBC-I. Participants were 36 parent-adolescent dyads. Adolescents received the Transdiagnostic Sleep and Circadian Intervention (TranS-C) as parents received the PBC-I. Dyads were assessed at pre- and post-intervention for parent use of behavior change techniques (BCT) and positive and negative conversational behaviors, parent-adolescent conflict, adolescent motivation for change, and adolescent sleep outcomes. From pre to post, parents used fewer total and types of BCTs, more positive communication behaviors, and less negative communication behaviors when discussing a sleep-related hot topic. From pre to post, parents reported decreased coercion and less anger intensity while adolescents reported fewer parental conflict behaviors and less quantity and anger intensity during parent-adolescent disagreement. There was a pre-to-post increase in interest/enjoyment of sleep and a decrease in effort/importance to participate in TranS-C. More positive and less negative communication was associated with select adolescent sleep outcomes. Parents rated the PBC-I as highly acceptable and perceived it as useful. These results provide preliminary evidence supporting the PBC-I improving the parent-adolescent interpersonal process, which is linked to improved adolescent sleep. The results may be relevant to conversations parents have with adolescents about a range of health behavior change.