The study findings substantiate previous studies in showing that parents with children in the child welfare system use substances at high rates; however, variables related to parental prenatal and postnatal substance use were not all significant predictors of child maltreatment and foster care placement transitions. The findings suggest that a mother's prenatal and postnatal substance use were not significant individual predictors of child maltreatment or foster care placement transitions. Significant links were found, however, between mothers' prenatal alcohol and drug use, fathers' postnatal substance use, child maltreatment, and foster care placement transitions. This suggests that the mother's prenatal substance use is related to the father's postnatal substance use, which is a significant risk for child maltreatment and foster care placement transitions. These two variables in combination (mother's prenatal substance use and father's postnatal substance use) should be targeted for child-maltreatment prevention and intervention. Study participants were 117 maltreated children (3- to 6-year-olds) recruited through the local child welfare system (Lane County, OR). The children's maltreatment experiences were coded from case files. Complete child welfare placement records were obtained for each child. Information on prenatal and postnatal parental substance use was obtained from caseworker files. These data were based on self-reports of family members and on information available to the caseworker at the time of the study. 1 table, 2 figures, and 71 references