Parents of children with intellectual and developmental disabilities generally report more stress than other parents. Child behavioural features, and specifically their behaviour problems, have been shown to account for some of the variation in parents' experience of stress. However, there has been no exploration of whether the child's pro-social behaviour is predictive of parenting stress. In the present study, 74 mothers of children with intellectual disabilities completed measures of stress and mental health and reported on their child's adaptive behaviour, problem behaviour, and pro-social behaviour. Regression analyses revealed that the child's behaviour problems were an independent positive predictor of maternal stress, the child's pro-social behaviour was a negative predictor of maternal stress, but adaptive behaviour was not a predictor. These results support the need for more research on the pro-social behaviours of children with intellectual disabilities, especially their putative impact on parental well-being.