Although substance abuse is one of the primary reasons that parents become involved with the child welfare system, there is surprisingly little empirical research that examines the relationship of substance abuse treatment to child welfare outcomes. In this statewide longitudinal study of 1911 women who had children placed in substitute care, we examined the influence of three key factors in the treatment process on child welfare outcomes. Results indicated that when these women entered treatment more quickly, spent more time in treatment, or completed at least one treatment episode, their children spent fewer days in foster care and were more likely to be reunified with their parents. These findings were significant even controlling for families' levels of risk including treatment and child welfare history, substance abuse frequency and chronicity, and demographic risks. Implications of these findings for improvements in the way that treatment services are provided to women in the child welfare system are discussed.