Objective This descriptive study examined the prevalence and correlates of trauma, substance use, and mental health symptoms in homeless transitional age youth (TAY) in San Francisco.

Design & Sample One hundred homeless TAY were recruited from a community‐based organization to complete a survey on trauma, mental health symptoms, and substance use.

Measurements We used these measures: National Institute on Drug Abuse (NIDA)‐Modified Alcohol, Smoking, and Substance Involvement Screening Test (ASSIST) for frequency and risk level of substance use; the 10‐item Adverse Childhood Experiences (ACEs) for prevalence of trauma; the Post‐traumatic Stress Disorder Checklist for DSM‐5 for post‐traumatic stress disorder (PTSD) symptoms; Center for Epidemiologic Studies Depression Scale for depression symptoms; and Generalized Anxiety Disorder 7‐item for anxiety symptoms.

Results Almost all (n = 98) participants experienced at least one ACE during childhood, and 77% experienced four or more. Most participants (80%) reached the diagnostic threshold for PTSD, 74% for depression, and 51% for moderate anxiety. Symptoms of PTSD, anxiety, and depression were all significantly correlated with use of opioids and stimulants.