Background Because of an increase in life expectancy and de-institutionalisation, many adults with intellectual disability (ID) live with and are cared for by their parents throughout their adult lives. Because of caring demands, the quality of life (QOL) of parents may be affected. The study explored the impact of caring for an adult with ID on the QOL of parents. Methods Participants were 12 parents who were the full-time carers of an adult with ID. Participants were interviewed about the effect of caring on their QOL. Interviews were analysed thematically. Results Caring had a positive impact on QOL by enabling participants to develop relationships and receive support, participate in leisure activities, achieve a sense of personal satisfaction and enable a more positive appraisal of their lives. Caring had a negative impact on participants' QOL by restricting their relationships, leisure activities and employment opportunities. Caring was also associated with financial insecurity, frustrations at the service system and fear of what the future held for their offspring. Conclusions Caring for an adult with ID had both positive and negative effects on parents' QOL. Improving services and service delivery, including the provision of residential services and respite, would address many of the issues that were reported to have a negative impact on parents' QOL.