This study explored whether variations in parenting provided by mothers with substance‐abuse disorders are related to behaviour problems in their young children and whether specific parenting practices are associated with specific types of behaviour problems. Mother‐reported and observational assessments were used to examine contributions of parenting behaviour and home environment to internalizing and externalizing behaviour problems in 150 preschool children of mothers receiving methadone‐maintenance treatment for heroin addiction. In multivariate analyses, mother‐reported child externalizing behaviour was related to greater maternal harshness and to mother history of illicit drug use during pregnancy but not other features of substance use and treatment history. Observer‐coded child internalizing behaviour was related to less maternal sensitivity and less provision of learning activities in the home. Additionally, mother report of her own psychopathology symptoms was related to mother‐reported, but not observer‐coded, child internalizing and externalizing problems. Findings suggest that women in substance abuse treatment should receive parenting interventions and that interventions should focus on increasing maternal sensitivity, reducing harshness, and providing children with cognitively stimulating environments. Findings also suggest that the need for attention to ongoing mental health problems of women in substance abuse treatment—both for their own well‐being and the well‐being of their children. Highlights This study explored whether variations in parenting provided by mothers with substance‐abuse disorders are related to behavior problems in their young children. Maternal harshness was related to child externalizing behavior, low sensitivity, and low provision of learning opportunities to child internalizing problems. Findings suggest that women in substance abuse treatment should be provided access to parenting interventions.