Although BMT is lifesaving in many childhood diseases, it was found to be related to anxiety, depression, and PTSD in parents, and PTSD, anxiety and overall low self-esteem in siblings. Research on siblings' HRQoL is limited. The aim of this study was to investigate PTSD and HRQoL in siblings (donor and non-donor) of pediatric BMT survivors and PTSD in their mothers, compared to the healthy controls. Thirty-five siblings and their mothers and 35 healthy peers and their mothers were recruited as the study group and as the comparison group, respectively. In children, Child PTSD-Reaction Index for PTSD and PedsQL for HRQoL were used. PTSD Checklist-Civilian Version was used for PTSD in mothers. The study group, both children and mothers, obtained significantly higher PTSD rates than the control group. Children in the study group also reported significantly poorer HRQoL than the control group in all scales. As a novel finding, there was a significant negative correlation between siblings' and mothers' PTSD scores and siblings' PedsQL scores, indicating that PTSD symptoms in siblings and mothers significantly led to impairment in siblings' HRQoL or vice versa. Thus, the identification and treatment of siblings and mothers with PTSD seems imperative.