The treatment response of 139 pregnant and postpartum women in gender-specific residential substance abuse treatment was investigated. These women were assessed with the Addiction Severity Index (ASI) at intake and six months after their discharge. A factor analysis performed with these women's ASI composite scores revealed two distinct factors: a substance use severity factor primarily from the alcohol and drug composite scores, and a general life distress factor primarily from the medical, legal, family/social and psychiatric composite scores. A cluster analysis of the pre- and post-ASI factor scores revealed four main subgroups of women (ranging in size from 14 to 41%) that had different patterns of change in response to treatment. Patterns of change could accurately be predicted for 71% of the women based on intake ASI severity composite scores, history of prior treatment, and service bundle received. (C) 2004 Elsevier Ltd. All rights reserved.