Accessible Summary People who have difficulties in communication and understanding are often excluded from research which is about them In our research, we wanted to find out how people with autism plus learning disability get on with their brothers and sisters once they are grown up We met with twelve people with autism along with their brother or sister without disability in a way that we hoped would make them feel relaxed Meeting the brothers and sisters with autism was important, and it helped us understand their relationships much better. It also helped us make suggestions about how they and their siblings could be better supported. Summary Adult siblings of people with autism and a learning disability have hitherto been largely overlooked by research, policy and practice in the UK. As part of a qualitative study focussing on adult siblings, we met twelve people with autism plus severe learning disability with their brother or sister. Individually tailored resources were used to make the meeting accessible and positive. Sibling involvement was essential to the participation, and inclusion of adults with autism plus learning disability strengthened the research findings, making them more valid and more relevant to policy and practice. This article describes our experiences of facilitating this involvement, the methods used and understandings gained, with the aim of encouraging practitioners and researchers to do likewise.