This study investigated how siblings of children with autism spectrum disorder (ASD) describe and define their quality of life. Using a qualitative research design, the authors collected data through a 4-stage process which included in-depth interviews of 17 children ages 6 to 14 and focus groups. All of the children with ASD were male and between the ages of 5 and 16 with mild to moderate impairments; all of the participating families lived in a Dutch-speaking region of Belgium. Analyzing data according to the principles of grounded theory resulted in the identification of 9 domains of sibling quality of life (SibQol). The apparent invisibility of ASD emerged as an important theme. Results indicate that siblings of children with ASD can define their quality of life, that unique characteristics of ASD give the siblings' experience a highly personal interpretation, and that the SibQol concept can be used to support siblings of children with ASD.