Maternal substance abuse and mental disorders can have adverse impacts on child development. We investigated the impact of maternal mental health on child behaviors based on a long-term follow-up study of mothers and their children approximately 10 years after mothers’ admission to drug abuse treatment. Mothers (n = 396) were assessed at admission to drug treatment during 2000–2002, and at follow-up in 2010–2011. At follow-up, each mother was asked to assess one target child using the Child Behavior Checklist for ages 6–18. Mothers’ mental disorder diagnoses were obtained from records maintained by the California Department of Mental Health in 2009. About 46 % of mothers had comorbid mental disorders; 27 % had depressive disorder, 15 % bipolar disorder, 15 % adjustment disorder, 13 % anxiety disorder, and 6 % psychotic disorder. Of these mothers, more than half had two or more mental disorder diagnoses. The average age of the target child was approximately 10 years old (range 6–17). Relative to children of mothers without comorbid mental disorders, children were more likely to demonstrate internalizing behaviors if their mothers had comorbid depression/anxiety disorders (OR = 2.0, 95 % CI 1.0–4.0) or severe mental disorders (psychoses, bipolar) (OR = 3.4, 95 % CI 1.5–7.6). For externalizing behaviors, family problems was the only significant predictor (OR = 3.2, 95 % CI 1.7–6.0 for children of mothers with depression/anxiety disorders, OR = 3.9, 95 % CI 1.9–7.8 for severe mental disorders). Addressing maternal mental disorders (particularly severe mental disorders) and family problems are important for child well-being as these factors were significantly related to emotional and problem behaviors of children.