Background: Most studies of siblings of individuals with autism have involved children or adolescents. In the present study we explored the experiences of adults with a brother or sister with autism. Method: As part of a larger scale, adult sibling study, 56 individuals (37 females, 19 males; mean age 40 years) were asked about their experiences of growing up with a sibling with autism and about their worries for the future. Results: Most participants (77%) described positive benefits, often related to the impact on their own life or personality (e.g. making them more tolerant or caring) and to the positive characteristics of their sibling with autism. Only 14% could describe no positive aspects. The principal problems described were related to coping with behavioural difficulties (39%) and disruption to family relationships (32%) or social life (23%). There was no association between the level of negative descriptions and individual sibling characteristics, participants' social functioning or mental health. The main concerns for the future, expressed by the majority of participants, focussed on problems of finding appropriate care (77%) and the potential emotional impact on the autism siblings of loss of parents. Conclusions: Most participants described a mix of positive and negative experiences but current concerns focussed predominantly on future longterm care. Many adult siblings will become increasingly responsible for ensuring the welfare of the individual with autism. Medical and other services need to recognise the importance of this role, and the need actively to involve siblings in care planning and decision-making.