In addition to the potential for ongoing health concerns, adolescent and young adult (AYA) childhood cancer survivors frequently report posttraumatic stress symptoms (PTSS). The current study examines whether beliefs about health moderate the relationship between the number of health problems and PTSS 2 months later in 140 survivors. Beliefs, as measured by scales of the Health Competence Beliefs Inventory (HCBI), negatively related to PTSS while health problems positively related to PTSS. Three scales of the HCBI-health perceptions, satisfaction with healthcare and cognitive competence—were significant moderators. The relationship between health problems and PTSS was stronger in the presence of less adaptive beliefs. These beliefs represent potentially malleable intervention targets for reducing PTSS in childhood cancer survivors.