Adolescent cannabis use is often accompanied by symptoms of a range of psychiatric disorders. This chapter offers an exploration of associations between cannabis use and psychological symptoms in adolescence, including psychotic symptoms, mood symptoms, anxious symptoms, neurodevelopmental symptoms, and use of other substances. Drawing on epidemiological evidence and clinical studies, this chapter summarizes the prevalence, clinical manifestations, and theorized mechanisms linking cannabis use to these mental health symptoms. Existing evidence supports bidirectional associations between cannabis use and psychiatric symptoms across diagnostic categories. Therefore, we suggest that cannabis use is an important clinical indicator for underlying mental health symptoms in adolescence.