Background: This study investigated whether care staff's causal attributions and emotional reactions to the challenging behaviour displayed by service users were influenced by the service user's diagnostic label. Materials and Method: One hundred and twenty care staff were randomly allocated to one of three conditions. Participants viewed a video of a senior staff member describing a service user, varying only in diagnostic label (autism, learning disability or Down syndrome). Participants then rated their endorsement of possible causes and emotional reactions to challenging behaviour. Results: Participants in the Autism and Down syndrome groups made more use of biomedical causes and less use of learned behaviour as an explanation for challenging behaviour than those in the Learning Disabilities group. Those in the former groups reported more positive and fewer negative emotions than those in the Learning Disabilities group. Conclusions: The way staff viewed people with learning disabilities was affected by their diagnostic label. Implications for further research and training have been discussed