BACKGROUND: Many childhood cancer survivors (CCS) experience cancer-related worries (CRW), for example about late effects and cancer recurrence. CRW are associated with lower quality of life (QoL) and maladaptive health care use. We examined the prevalence, severity, and factors associated with CRW in adult CCS. METHODS: We included quantitative studies of ≥ 100 participants reporting on prevalence, severity, mean scores and/or associated factors of CRW among CCS aged ≥ 18 years, diagnosed at ≤ 21 years, and ≥ 2 years post-diagnosis. We searched MEDLINE/PubMed and APA PsycINFO, hand-searched reference lists, and consulted experts. Risk of bias was assessed using the Cochrane Childhood Cancer Risk of Bias Criteria. Results were synthesized descriptively. RESULTS: The 17 included studies with a total of 26,306 CCS identified three main themes of CRW: health-related, financial, and interpersonal. Most prevalent were health-related worries regarding future health (88%-92%), late effects (83%), cancer recurrence (25%-88%), second cancers (50%-91%), and infertility (34%-68%). Factors associated with increased CRW varied depending on the specific CRW. These included female sex, more pain, anxiety, depression, chronic conditions (e.g., neurologic, being overweight), and treatment history (chemotherapy, radiotherapy). DISCUSSION AND IMPLICATIONS: Although most included studies used single items to assess CRW, this review underscores that health-related worries are particularly prevalent among CCS. Effectively identifying CCS at high risk, for example through using validated measures, and addressing severe CRW can facilitate adaptive healthcare use and improve QoL among CCS. Potential interventions can be providing information about late effects, psycho-education, discussions during follow-up care, and targeted psychosocial support for those with severe CRW.