Children of depressed mothers have been shown to express behaviour problems to a greater extent than children of non-depressed mothers. The purpose of this study was to examine the persistence of depressive symptoms in mothers and to evaluate the relative importance of symptoms of postpartum depression (PPD) and concurrent maternal symptoms of depression, on child behaviour at age 12. A birth cohort of 1,707 children and their mothers was followed from 3 months after birth to 12 years after birth. Self-reported symptoms of depression in mothers were assessed at baseline and 12-year follow-up where 893 mothers (52.3 %) and their children participated. The mothers' reports on the behaviour of their children at age 12 were used. Multivariate analysis was used to assess factors that increased the risk of child behaviour problems. At baseline, 10.4 % scored above the cutoff for symptoms of postpartum depression. At follow up, 18.2 % scored above the cutoff for depressive symptoms. Multivariate analysis showed that ongoing maternal symptoms of depression, as distinct from PPD-symptoms, was the strongest predictor of child behaviour problems at age 12. The gender of the child and socio-demographic factors at baseline were additional factors that affected the risk of behaviour problems in the 12 year old children. Children of mothers who reported symptoms of depression, both postpartum and at follow-up, were at a greater risk of behaviour problems compared to children of women with no depressive symptoms on either occasion. Our findings indicate that recurrent and ongoing maternal depressive symptoms significantly increase the risk of child behaviour problems as reported by mothers, while symptoms of PPD do not seem to result in an increased risk of behaviour problems in 12 year olds. High maternal socio-demographic life stress at childbirth constitutes an important risk factor for later child behaviour problems.