Background: Can ratings of temperament be a way of identifying young children with intellectual disabilities (ID) who are at risk for being experienced as difficult? We aimed to explore parents' reports of temperament in their young children with or without ID, as well as positive and negative impact of the child on parents. Method: Mothers and fathers of 55 children recently diagnosed with ID and 183 age-matched typically developing (TD) children completed the EASI Temperamental Survey and two scales of the Family Impact Questionnaire measuring positive and negative impact of the child on parents. Results: Parents rated children with mixed ID/DD (developmental delay) as shyer and more impulsive, and less active and sociable when compared with TD children. Children with mixed ID/DD were also reported to have more negative and less positive impact on the family compared with the TD group. In subgroup analyses, children with Down syndrome and cerebral palsy/motor impairment were described as having less negative impact on parents and were described as low in negative emotionality. Children with autism spectrum disorder (ASD), ID/DD nos and other less common diagnoses had a similar pattern of temperament with high emotionality, shyness and impulsivity, and low activity and sociability. Parents of children with ASD and ID/DD reported the highest level of negative impact. Conclusions: Temperamental characteristics such as high negative emotionality and impulsivity, which can be identified earlier than behavioural problems, could be indicators of negative impact on parents of young children with ID. Despite great variability in temperament among children with mixed ID/DD, results indicated common temperamental characteristics among children with ASD, ID/DD and other diagnosis.