BackgroundMaternal mental health conditions within the postnatal period can have long-lasting consequences on a child’s well-being. This study synthesises current evidence on the association between postnatal maternal mental health-related hospitalisation (MHrH) and adverse child health and maltreatment outcomes.MethodsWe conducted an inclusive search across multiple databases, including MEDLINE, PsycINFO, CINAHL, Scopus, Embase, Google Scholar, and the reference list of eligible papers. Studies that used standardised outcome measures were included. Study selection and data extraction were made using a standardised Joanna Briggs Institute (JBI) tool. The quality of the studies was assessed using the Newcastle-Ottawa Scale (NOS). Descriptive vote counting to map the direction of effects, alongside narrative thematic synthesis, was used to summarise the findings from the included studies.ResultsFour studies (n = 1,020,342) were included in the review. Three of these studies suggest a possible association between postnatal maternal MHrH and adverse child health outcomes (growth failure, respiratory and gastrointestinal infection) or maltreatment (sexual, physical, and emotional abuse). One study did not find a statistically significant association between postnatal maternal MHrH and infant growth.ConclusionThe available evidence suggests a possible association between postnatal maternal MHrH and adverse child health and maltreatment outcomes. However, given the small number of studies and methodological heterogeneity, these findings should be interpreted cautiously and highlight the need for further high-quality longitudinal research.Systematic Review Registrationhttps://www.crd.york.ac.uk/prospero/, identifier CRD42023446155.