The Addiction Severity Index (ASI) is a widely adopted assessment instrument that provides severity ratings of the multiple problems exhibited by alcohol and drug dependent persons and allows for quantitative assessment (composite scores) of client status in these problems areas over time. ASI change scores of homeless and near homeless substance abusers, generated by contrasting ASI composite scores at two points in time, show a high level of agreement to objective relapse data from the Massachusetts Bureau of Substance Abuse Services Management Information System. Clients readmitted to a publicly funded detoxification facility exhibited significantly lower mean change scores on five of the seven problems areas measured by the ASI. These data illustrate the applicability of the ASI to homeless men and women and the utility of the ASI in measuring client improvement.