Sleep and behavioural difficulties are common in children with developmental disabilities. Mothers often wake and tend to their child when their child is having sleep difficulties. Therefore, mothers of children with developmental disabilities can have poor sleep quality due to these disruptions. The present study investigated the impact of sleep and behaviour problems in children with developmental disabilities on mothers' sleep quality and psychological wellbeing. The sample consisted of 46 mothers and 50 children with developmental disabilities. The results indicated that greater sleep and behaviour problems in children were significantly associated with disturbed sleep and increased depression, anxiety and stress levels in mothers. Mothers' sleep disturbance was also found to significantly predict poor maternal psychological wellbeing. The research limitations, implications of findings, and directions for future research are also discussed. (Contains 3 tables.)