This study compared maternal responsiveness to children with two neurodevelopmental disorders sharing different but, in some cases, overlapping social phenotypes--Williams syndrome (WS) and autism spectrum disorder (ASD)--and explored the relations between maternal responsiveness and child emotional/behavioural problems (EBP). The sample included 16 pre-schoolers with WS and 43 with ASD, and their mothers. Responsiveness was assessed during a mother-child interaction task. Mothers completed the CBCL 1½-5, providing a measure of EBP. No significant differences emerged between groups, and most dyads were characterized by less responsive behaviours. Maternal responsiveness proved related to child developmental age, but not with EBP. These results provide further insight into the rearing environment of children with neurodevelopmental disorders, highlighting the need for early relationship-based interventions.