Background: Siblings of children with cancer may experience adverse household economic and psychosocial impacts during and after treatment. While many long-term survivors of childhood cancer experience financial hardship, financial outcomes of siblings in later adulthood are unknown. Methods: We surveyed randomly selected nearest age siblings of survivors (aged 18-64y) enrolled in the CCSS to estimate the prevalence of financial hardship, using 20 items adapted from validated national surveys grouped into 3 domains (material, psychological, behavioral). We calculated the prevalence of reporting any hardship within each domain. Multivariable logistic regression estimated associations between sibling sociodemographic characteristics and each domain of hardship. For individual financial hardship items with a matching item in the contemporaneous National Health Interview Survey (n = 21,271) or Behavioral Risk Factor Surveillance System (n = 259,901), we compared siblings with national survey respondents aged 18-64, calculating adjusted prevalence ratios to sample-weighted responses, adjusted for sex, race, ethnicity, household income, education, and marital status. Results: 1,008 siblings participated (of 1,590 approached; 63%) with median age of 46y (IQR 39–53y). Siblings were 57% female, 89% non-Hispanic White, 69% college-educated, and 74% married. The prevalence of reporting any material, psychological, and behavioral hardship among siblings was 34%, 28%, and 23%, respectively. Sibling factors associated with reporting material financial hardship included: female sex (OR 1.7, 95% CI 1.2–2.4), age (30–39y vs 21–29y: OR 2.61, 95% CI 1.1–6.5), household income ($50,000–$74,999 vs ≥$75,000: OR 2.3, 95% CI 1.4–3.6), lack of health insurance (OR 2.4, 95% CI 1.1–5.1), presence of severe/disabling chronic medical conditions (OR 1.7, 95% CI 1.1–2.8), out-of-pocket medical expenses ≥10% of income (vs < 10%: OR 4.9, 95% CI 1.9–12.3), and increased non-medical/non-home debt (for example, $25,000–$49,999 vs none: OR 5.2, 95% CI 3.2–8.6). Associations with psychological and behavioral hardship were similar. Compared with national survey respondents, siblings were more likely to report financial hardship on several individual items: difficulty paying medical bills (PR 1.2, 95% CI 1.0–1.4), worries about bills (PR 1.1, 95% CI 1.1–1.2), foregoing medical care (PR 1.3, 95% CI 1.0–1.6) and dental care (PR 1.4, 95% CI 1.2–1.6) due to cost, and worries about affording nutritious foods (PR 1.7, 95% CI 1.5–2.0). Conclusions: Adult siblings of childhood cancer survivors are more likely to experience multiple aspects of financial hardship than US adults in the general population, suggesting that childhood cancer may have life-long impact on siblings. Increased support for families across the trajectory of cancer treatment may help prevent or reduce financial hardship.