The purpose of this study was to compare females who were concurrent clients of two different services–-Alcohol and Drug (AOD) Treatment and Child Protective Services (CPS)--with those who were only clients of AOD treatment. The study used clients who received treatment over a 3 year period (1997-99) in public AOD programs in San Diego County, California, with a specific focus on the CPS clients within this group. Results showed that women who were involved with substance abuse treatment and CPS were younger, had more children, had been arrested less often, were mandated to receive treatment, had an unsatisfactory exit status, and were transferred to another treatment program at discharge. These women were also more likely to have attended outpatient or day treatment for the AOD treatment, perhaps due to childcare and/or custody issues. The implications of this study are that service providers in AOD treatment need to target the youngest women, particularly those with children, as a prevention strategy against child maltreatment. Childcare may be needed to help young mothers use AOD treatment services. Another implication is that AOD treatment sources and CPS must work closely together. Treatment failure may reflect the fact that service providers were not yet fully prepared to treat the multiple problems of these families. It is possible those families in which AOD was occurring who were brought to the attention of child protective service agencies may reflect a more problem-ridden, chronic sub-population within the larger problem of child maltreatment. Since treatment failure was associated with mandated treatment, a greater use of voluntary plans by CPS is warranted. There are some systems issues that need attention by policy makers, such as concurrent planning mandates in child welfare. 6 tables, 46 references