A total of 60 children between 8 and 15 years of age participated in this project, 20 of whom had a sibling with autism, 20 a sibling with mental retardation and 20a non-disabled sibling. The children were questioned about their sibling relationship and their experiences of stress. The children with a sibling with autism also completed a questionnaire on their knowledge of the autistic syndrome. Analyses revealed that the three groups were basically similar in their ratings of the frequency of stressors involving their siblings. There was a trend for children with a disabled brother or sister to rate their relationship with the sibling more positively. Correlational analyses revealed an association between both stressor frequency and appraisal and the evaluation of the relationship with the brother or sister. Siblings of children with autism had a fair understanding of the autistic syndrome, in this group, there was also an association between the children's knowledge of the autistic disorder and the quality of the sibling relationship.