BackgroundMaternal substance use is considered a significant risk for child maltreatment and neglect, and thus, a common feature in care proceedings (Family Courts). It is important to better understand how the complex needs of these mothers impact on care proceedings’ outcomes. The present study explored individual and clinical characteristics of mothers receiving treatment for substance use to describe who the mothers involved in care proceedings are, and explore what factors are associated with out-of-home placement of their children. MethodsData were extracted from electronic health records (EHRs) of 1587 mothers of dependent children (age < 18 years old) who attended South London and Maudsley (SLaM) National Health Services (NHS) Foundation Trust addiction services between 2007 and 2019. Clinical service records of 480 mothers (30 %) were linked to family court records. ResultsThe number of care proceeding cases decreased during the study period. Most mothers involved in care proceedings (79 %) were known to SLaM before care proceedings began. Compared to mothers who were not involved in care proceedings, mothers who were involved, were more likely to be younger, from a non-white background, to be socially deprived, to experience housing problems, to be pregnant, to have a longer duration of treatment for substance use, to use opioids and/or crack-cocaine and to report lifetime domestic violence victimisation, be at risk of suicide, and report poorer quality of life and psychological health. The median length of care proceeding cases was 37 weeks. Eighty-two percent of mothers had care for their child terminated by the court. Mothers’ younger age, housing problems, use of opiate and/or cocaine/crack-cocaine and poorer quality of life increased the odds of out-of-home placement of the children. The participation of the child’s father in the proceedings was a protective factor for maintaining care of the child for those mothers that were receiving substance use treatment at the time of the proceedings. Attending treatment for substance use during the proceedings was not associated with the child placement outcome. ConclusionFindings highlight that current substance use treatment services are not designed to support mothers retain the care of their children. Understanding and addressing the range of needs of these mothers has implications for both substance use treatment and child welfare.