Aims. This study assesses the viability of a self-administered version of the Addiction Severity Index for monitoring substance abuse patients' functioning. Design and measurements. Patients completed the ASI interview and a self-administered questionnaire containing ASI composite items an average of 4 days apart. Composite scores from both formats were compared using correlations and mean differences. Participants and setting. Participants were 316 veterans entering substance abuse treatment in a US Department of Veterans Affairs medical center. Findings. Composite scores for alcohol, drug, psychiatric, family, legal and employment problems correlated 0.59-0.87 across formats. Patients endorsed more drug use and psychiatric symptoms by questionnaire than by interview. Medical composite scores correlated only 0.47 across formats. Conclusions. This study and previous research suggest that a self-administered questionnaire can be a feasible alternative to ASI interviews for monitoring substance abuse patients' treatment outcomes.