Substance use, including methamphetamine use, is a contributing factor in HIV acquisition and treatment. Stimulant use is linked to mental health yet there is limited data from youth in community-based settings. One hundred marginally housed or homeless transitional age youth (TAY) were recruited at Larkin Street Youth Services and completed a survey on mental health and substance use. We conducted secondary data analysis using multivariable logistic regression models to identify the correlates of methamphetamine use among TAY. The participants' mean age was 22. Of those who reported methamphetamine use in the past 3 months, 64% were Gay, Bisexual, or Pansexual. Factors independently associated with methamphetamine use were; living with HIV (adjusted odds ratio [aOR]=3.18, 95% CI=1.11-9.15), depressive symptoms (aOR=6.02, 95% CI=1.46-24.78), symptoms of PTSD (aOR=13.38, 95% CI=1.59-112.73), polysubstance use in the past 3 months (aOR=50.02, 95% CI=9.72-257.46) and a history of injection drug use (aOR=8.38, 95% CI=1.87-37.53). Results from this study suggest a need to develop, adapt, and rapidly implement comprehensive interventions that address the combined epidemics of substance use, HIV, and mental health among TAY. This article examines factors associated with methamphetamine use among transitional age youth (TAY) experiencing homelessness or housing instability. Several factors were associated with use, including depression, PTSD, HIV status, polysubstance use, and injection drug use. These findings highlight the need for nurses to assess for methamphetamine use among youth as well as associated mental health and physical health problems. Nurses should link TAY who are using methamphetamine to evidence-based treatment programs to address substance use and comorbid conditions.