Despite often being mandated to substance use treatment after release, many people on probation do not complete treatment. Several historical factors have been identified as relevant to substance use treatment in this population (i.e., past substance use, treatment history, and criminal history); however, less is known about the psychological characteristics, such as emotion dysregulation, that influence treatment-relevant factors among people in the criminal justice system. The present study used cross-sectional data to examine whether emotion dysregulation was associated with past-year substance use severity, engagement in prior drug and alcohol use treatments (yes/no, number of prior treatments), and previous criminal charges (total number of charges, number of charge types) in a sample of adults on probation who were receiving court-mandated substance use treatment (N = 163). We also examined whether these relationships varied across sex. Results showed that overall emotion dysregulation was more strongly linked to substance use severity and criminal charges for females than males. Emotion dysregulation dimensions of difficulties engaging in goal-directed behaviors and controlling impulsive behaviors when distressed were associated with more severe past-year substance use, more prior drug treatments, and a greater number of lifetime criminal charges and charge types. Emotion dysregulation plays a role in substance use treatment-relevant factors among people on probation. Sex-specific clinical implications of targeting emotion dysregulation in the context of mandated treatment in order to prevent treatment failures are discussed. (PsycInfo Database Record (c) 2024 APA, all rights reserved).