Objectives: The objective of this work was to assess the reliability and validity of the Treatment Motivation Questionnaire-Revised (TMQ-R) in people with serious mental illness (SMI). Method: A large sample of consumers of mental health services (n = 469) were administered the TMQ-R. Results: The factor structure specified in previous research did not fit the data well. However, a five-factor model with the two subtypes of introjected (i.e., feeling guilty about not attending treatment) and external motivation (i.e., pressure to attend treatment) fit the data well. Conclusions: The current analyses partially confirm the TMQ-R structure and reflect the need for future work to evaluate the complexities of motivational measurement within people with SMI. (Contains 3 tables.)