The probands of this study were 60 children and young adults between 5 and 20 years of age, 20 of whom had siblings with autism, 20 of whom had siblings with mental retardation, and 20 of whom had siblings who were free of handicap. The three proband groups were matched for gender, birth order and socioeconomic status. The children were questioned about their sibling relationships and about particular problems they faced concerning their handicapped brothers or sisters and about problems concerning themselves. Parents were interviewed about the healthy child's behaviour and social adjustment. Mothers completed the Eysenck Personality Inventory concerning themselves. Siblings of handicapped children and especially siblings of children with autism were more concerned about the future. They also felt lonely more often and many of them had peer problems. They often regarded their handicapped siblings as a burden. They tended to have only one sibling. Siblings often did not know why their handicapped brother or sister was different from other children. There were more behaviour disturbances in the siblings of handicapped children and mothers with a child with autism reported more ‘stressful events’. There were no differences as regards the personality of the mothers and the self-concept of the children between the three groups.