Hematopoietic stem cell transplantation (HSCT) is an accepted medical treatment for many serious childhood diseases. HSCT is a demanding procedure that creates both physical and emotional challenges for patients and their family members. Research has demonstrated that siblings of children undergoing HSCT are at risk for developing psychosocial problems such as posttraumatic stress, anxiety, and low self-esteem. This study examined psychosocial changes in siblings ("N" = 30) of pediatric HSCT recipients. These siblings participated in an art therapy intervention session 1 week, 1 month, and 3 months after their siblings' HSCT procedure. Results showed improvements in sibling psychosocial functioning associated with participation in the art therapy interventions. Compared to a control group ("n" = 10), the intervention group ("n" = 20) showed lower levels of posttraumatic stress symptoms at the final session.