BackgroundSiblings of children with cancer may experience adverse household economic consequences, but their financial outcomes in adulthood are unknown.MethodsA total of 880 siblings (aged 18–64 years) of adult‐aged childhood cancer survivors were surveyed to estimate the prevalence of financial hardship by three established domains (behavioral, material, and psychological). For individual financial hardship items matching the contemporaneous National Health Interview Survey or Behavioral Risk Factor Surveillance System, siblings were compared with the general population by calculating adjusted prevalence odds ratios (ORs) to sample‐weighted responses. Multivariable logistic regression models examined associations between sibling characteristics and each hardship domain and between sibling hardship and survivors’ cancer/treatment characteristics.ResultsBehavioral, material, and psychological hardship was reported by 24%, 35%, and 28%, respectively. Compared with national survey respondents, siblings were more likely to report worries about medical bills (OR, 1.14; 95% confidence interval [CI], 1.06–1.22), difficulty affording nutritious foods (OR, 1.79; 95% CI, 1.54–2.07), and forgoing needed medical care (OR, 1.38; 95% CI, 1.10–1.73), prescription medications (OR, 2.52; 95% CI, 1.99–3.20), and dental care (OR, 1.34; 95% CI, 1.15–1.57) because of cost. Sibling characteristics associated with reporting financial hardship in one or more domains included female sex, older age, chronic health conditions, lower income, not having health insurance, high out‐of‐pocket medical expenditures, and nonmedical/nonhome debt. No survivor cancer/treatment characteristics were associated with sibling financial hardship.ConclusionsAdult siblings of childhood cancer survivors were more likely to experience financial hardship compared with the general population. Childhood cancer may adversely affect entire households, with potentially lasting implications.