Age, employment status, primary drug of choice, and involvement in the legal system were significant factors that influenced the likelihood of completing substance abuse treatment. Older substance users were more likely to complete treatment, as were those who were employed. Heroin users were significantly less likely to complete treatment compared with alcohol, cocaine, and marijuana users. Also, parents/caregivers involved with the adult correctional system were more likely to complete substance abuse treatment. The children of substance-using parents/caregivers who do not successfully complete treatment have longer stays in substitute care settings, increasing the risk of the termination of parental rights. In order to increase the chances of family reunification, child welfare agencies, in collaboration with other appropriate community agencies, should address factors that tend to undermine the completion of substance abuse treatment for parents. The study sample consisted of 871 caregivers enrolled in the Illinois Alcohol and Other Drug Abuse waiver demonstration between April 28, 2000, and March 30, 2004. Approximately 22 percent of these caregivers completed all required phases of substance abuse treatment. Two sources of data were used to identify factors related to failure to complete treatment. First, certified clinicians conducted a computerized assessment that included information on a wide range of demographic and family characteristics, health and mental health status, drug dosage, and drug-use patterns. Information on drug use included primary drug of choice. Second, data on parents' status in substance abuse treatment were obtained from the Treatment Alternative for Safe Communities. 6 tables and 62 references