High rates of relapse following treatment have compelled researchers to elucidate the individual difference factors that change among those who receive substance abuse treatment. Previous research has suggested that trait-disinhibition variables may be of particular relevance. Given that these variables are primarily considered to be trait-level factors, the extent to which they are malleable by treatment is an important consideration. Thus, the purpose of this study was to examine the effect of a residential substance abuse treatment program on specific trait-disinhibition variables (e.g., risk-taking, impulsivity). A sample of 81 inner-city substance users were assessed on self-report and behavioral indicators of trait-disinhibition over a 30-day course of treatment. Risk-taking propensity was found to significantly decrease from pre- to post-treatment. Results are discussed with respect to implications for better understanding the factors that may operate as mechanisms of change during treatment, thereby having the potential to inform substance abuse prevention and treatment programs.