This study examines how parents and adolescents communicate about alcohol and marijuana during mid-to-late adolescence, a period marked by rising substance use risk. Although many parents want to reduce harm, they often receive unclear guidance, and what parents intend to convey may not align with what adolescents perceive. Building on prior work showing that alcohol-specific communication is multidimensional and meaningfully linked to youth drinking outcomes, this study surveys parent–adolescent dyads (ages 15–18) to assess the content, frequency, and perception of substance-related conversations. The study also extends prior research by directly comparing parent and youth reports to identify alignment and discrepancies in communication. In addition, it addresses a major gap by characterizing marijuana-specific parental communication, which remains understudied despite increasing adolescent use. Finally, the study tests whether parents' trauma histories, particularly trauma involving substance use, shape how and what parents communicate to their children about alcohol and marijuana.