Background: The present study aimed to clarify the circumstances under which maternal depression is associated with adverse outcomes in pre-school-aged children, and to explore the additional impact of the marital relationship in a socio-economically low-risk sample. Methods: Ninety-two mothers recruited into a longitudinal study were assessed for symptoms of depression when their children were 4, 12 and 15 months, and later at 4 years of age. At 4 years of age, mothers were also asked to report on marital adjustment. Mothers, fathers and pre-school teachers were asked to report on children's internalizing and externalizing behaviour problems. Results: Children exposed to chronic maternal depression were rated by their parents as significantly more problematic on internalizing and externalizing behaviours. This association was not mediated or moderated by low marital satisfaction. No parent-reported effects were evident for children exposed to transient depression. Ten per cent of the children had internalizing scores in the clinical range, and 7% had externalizing scores in the clinical range. Almost all of the children with clinically elevated scores had been exposed to chronic maternal depression. Teacher reports of internalizing behaviours corroborated parent reports; however, teachers tended to report significantly lower levels of behaviour problems. Although there was a tendency for teachers to rate children exposed to any depression as more problematic on internalizing behaviours, the subgroup differences were not significant. Conclusions: Findings confirm that depression chronicity is important in determining child behavioural outcomes, and that depression effects cannot be accounted for by low marital adjustment. Results are discussed with reference to transmission of risk models, and treatment implications are considered.