Background This study explored psychological adjustment and sibling relationships of siblings of children with life‐limiting conditions (LLCs), expanding on previous research by defining LLCs using a systematic classification of these conditions. Methods Thirty‐nine siblings participated, aged 3–16 years. Parents completed measures of siblings' emotional and behavioural difficulties, quality of life, sibling relationships and impact on families and siblings. Sibling and family adjustment and relationships were compared with population norms, where available, and to a matched comparison group of siblings of children with autistic spectrum disorder (ASD), as a comparable ‘high risk’ group. Results LLC siblings presented significantly higher levels of emotional and behavioural difficulties, and lower quality of life than population norms. Their difficulties were at levels comparable to siblings of children with ASD. A wider impact on the family was confirmed. Family socio‐economic position, time since diagnosis, employment and accessing hospice care were factors associated with better psychological adjustment. Conclusions Using a systematic classification of LLCs, the study supported earlier findings of increased levels of psychological difficulties in siblings of children with a LLC. The evidence is (i) highlighting the need to provide support to these siblings and their families, and (ii) that intervention approaches could be drawn from the ASD field.