To date, few studies have examined the effect of interagency collaboration on substance abuse assessment and treatment completion for parents who are involved in child welfare. The purpose of this paper is to: (1) describe a statewide, interagency collaborative program aimed at providing targeted substance abuse assessment and treatment to parents engaged in the child welfare system; (2) document the specialized assessment and treatment outcomes for parents engaged through this collaborative program; and (3) determine factors related to successful treatment completion for parents involved in the child welfare system. This is a retrospective study of an open cohort of 13,829 individuals admitted to the New Jersey Child Protection Substance Abuse Initiative (CPSAI) program from October 1, 2009, through September 30, 2010. Data were drawn from two unique administrative data sources. Multivariate Cox regression models were used to explore factors related to successful treatment completion for parents involved in the child welfare system. Trend analysis for the total sample in the CPSAI program revealed that, of the 10,909 individuals who received a CPSAI assessment, 59% were referred to treatment. Of those referred to treatment, 40% enrolled in a treatment program. Once enrolled in a treatment program, 55% completed or were in the process of completing substance abuse treatment. These findings suggest that when adequate screening and treatment is available through a streamlined process, many of the ethnic and gender disparities present among other populations of individuals seeking treatment are minimized. Utilizing inherent child welfare case factors appears to be an important motivating element that aids parents during the assessment and treatment process.