Studies of community-based treatment programs for substance users document that motivation for treatment is a consistent predictor of clients remaining under treatment for a longer period of time. Recent research has replicated this in prison-based treatment programs, implying that motivation is clinically important regardless of setting. The current study examines predictors of treatment motivation using data collected from 661 male drug-involved inmates during in-depth interviews that include components of the Addiction Severity Index, TCU Motivation Scale, and the Heath Services Research Instrument. Findings showed treatment motivation can be measured effectively in prison-based settings. Motivation scores were not significantly different between individuals in a prison-based treatment program and those in the general prison population. Furthermore, higher motivation for treatment scores were associated with greater levels of problem severity, suggesting that individuals with more drug-use related life problems may recognize this need and desire help for beginning long-term recovery.