['Previous research has linked family sleep disruption and dysfunction in children; however, the mechanism is unknown.', 'This study examined whether maternal sleep and postnatal depression (PND) mediate the relationship between infant sleep disruption and family dysfunction.', 'Mothers of infants aged 12 months old (N=111; 48% male) completed infant and parent sleep surveys, the Edinburgh Postnatal Depression Scale and the Family Assessment Device.', 'Poor infant sleep was related to poor maternal sleep, which was associated with higher PND and higher level of family dysfunction.'] Does postnatal depression mediate the relationship between infant and maternal sleep disruption and family dysfunction?