Background: Maternal depression is a risk factor for adverse outcomes in the child, including emotional and behavioural difficulties. There is evidence that child care attendance during the preschool years may moderate associations between familial risk factors and child outcome. However, the possibility that high-quality child care provides protection for children exposed to maternal depression or that low-quality child care provides additional risk has not been investigated. We study whether child-care quality moderates the association between probable history of maternal depression (PMD) and child behavioural and emotional outcomes over the preschool period. Methods: Within a longitudinal study, we examined PMD (no depression; clinical PMD before the child's birth; subclinical PMD from 0 to 5 years; clinical PMD from 0 to 5 years), child-care quality and child emotional and behavioural difficulties at the ages of 2, 3 and 4 years. Child-care quality was evaluated in settings, and trajectories were calculated to reflect (a) global quality and (b) two quality subfactors: 'Teaching and interactions' and 'Provision for learning'. Data were analysed for 264 families. Results: Significant interactions emerged between clinical PMD and global quality of child care for children's externalising behaviour (b = -.185, p = .008), more specifically hyperactivity/inattention (b = -.237, p = .002). In the context of clinical PMD, children attending high-quality child care presented fewer difficulties than those attending a low-quality care. Child-care quality was not associated with outcomes for children whose mothers did not report a PMD or a PMD before their birth. Conclusions: In the context of PMD, high-quality child care was associated with fewer behavioural problems and may thus constitute a protective factor. (author abstract)