This study asks which siblings of children with cancer (SCC) benefit most from a group intervention specifically designed for them. One hundred and eleven SCC (aged 8-17) participated in eight weekly 2-hour manualized group sessions. Changes in anxiety and depression symptoms were used as outcome measures. Anxiety and depression scores improved more for siblings who were initially most depressed and, thus, considered “less resilient” (p<0.0001). Within this group, males improved more than females and siblings of children with brain tumors improved less than SCC with other cancers, (p=0.05), with female siblings of children with brain tumors improving the least (p=0.0397).