A classification and regression tree (CART) analysis was applied to data for 237 male participants (M = 31.93 years, SD = 7.64) in a prison-based substance abuse treatment program to study the integrity of the Stages of Change model of treatment readiness. Using the Stages of Change Questionnaire (STOCQ), participants were assigned to Contemplation (102), Action (118), or Maintenance (17) groups. A CART analysis then examined differences in the overall group profiles on the basis of scores on the Psychological Inventory of Criminal Thinking, the Situational Confidence Questionnaire, and the Carlson Psychological Survey. The assumption of discrete stages of change was not supported. Alternative models are suggested: one based on states of change and one on personality characteristics. A focus on equal attention to both cognitive and behavioral aspects of substance abuse treatment readiness is suggested.