BACKGROUND: Polysubstance use is common among people who use methamphetamine. This prospective study examined the three-month polysubstance use profiles among people enrolled in outpatient treatment for methamphetamine use and associated substance use, mental health, and treatment correlates. METHOD: The present study used routinely collected client-reported outcome measures data from FINDINGS: Repeated measures latent class analyses revealed four classes: (1) high and decreasing methamphetamine + stable moderate alcohol + stable high cannabis and daily tobacco ( CONCLUSION: Individuals enrolled in outpatient treatment who report methamphetamine as their primary drug of concern report distinct substance use patterns, although daily tobacco use was mostly ubiquitous. Polysubstance use was widespread, with 79% of participants having moderate-to-high probability of polysubstance use at all timepoints. Clients with the most severe polysubstance use had the highest rates of co-occurring psychopathology.