Background: Existing research studies suggest that parenting a child with intellectual disabilities (ID) can be a stressful experience. However, there are few data addressing the question of how or why parents might experience considerable distress. In the present study, psychological variables (acceptance, mindfulness, avoidant coping) are explored that may explain some variance in maternal distress. Method: Questionnaire data were gathered from mothers of children attending special schools at two time points, 18 months apart (n = 91 at Time 1; n = 57 at Time 2). In addition to measures of the child's functioning, the questionnaire pack included: a measure of acceptance of unwanted thoughts/feelings; a measure of attention to the present (mindfulness); a measure of active avoidance coping; measures of maternal anxiety, depression and stress; and a measure of mothers' positive perceptions of their child. Results: In cross-sectional analysis, acceptance was negatively associated with maternal anxiety, depression and stress, such that mothers who were generally more accepting reported fewer psychological adjustment problems. Longitudinal analysis showed that acceptance is bidirectionally related to anxiety and depression. Mindfulness was not significantly related to maternal distress, and avoidance coping was positively cross-sectionally associated with depression only. There were no associations between psychological variables and maternal positive perceptions. Conclusions: These data suggest that acceptance, in particular, may be a construct that explains some variance in maternal distress. Further research could focus on the utility of acceptance-based interventions (e.g. Acceptance and Commitment Therapy) in the support of families with a child with ID.