Background: The behaviours of 24 mothers of children with fragile X syndrome (FXS) with their affected children were examined during planned observations in their homes. The goal of this study was to describe concurrent maternal interactive behaviour and the factors that influence the type and frequency of these behaviours within this group. Methods: The frequency of "maintaining," "directive" and "scaffolding" behaviours and the extent to which the mothers displayed "warm sensitivity" and "restrictions" were examined within a 60-min naturalistic observation and a 10-min toy play observation. Rating scales and parent questionnaires were used to assess selected maternal mental health factors, including depression, anxiety, stress and social support. The cognitive status of mothers and developmental and behavioural abilities of children were also examined. Results: The women in this study used primarily maintaining behaviours in interactions with their children. Maintaining behaviours and warm sensitivity were consistent across structured and unstructured settings, while directive, scaffolding and restricting were not correlated across the two settings. Child receptive language skills were related to higher rates of maintaining and scaffolding behaviours. The women reported clinically significant levels of stress, depression and anxiety at a prevalence rate higher than that of the general public. Child behaviour problems contributed to maternal stress, and mothers with higher stress engaged in fewer interactions with their children. Conclusions: The relations between maternal stress, child problem behaviour and number of interactive behaviours exhibited by the mothers in this study provide information that can inform interventions and provide direction for future research exploring environmental influences on the development of children with fragile X syndrome.