Purpose To estimate the incidence of late-occurring venous thromboembolism (VTE) among survivors of childhood cancer and to identify risk factors for VTE to facilitate diagnosis and prevention. Methods The Childhood Cancer Survivor Study is a multi-institutional cohort of 24,355 5-year childhood cancer survivors (diagnosed between 1970 and 1999; median age at last follow-up, 28.7 years [range, 5.6 to 58.9 years]; median follow-up since diagnosis, 21.3 years [range, 5.0 to 39.2 years]) and 5,051 sibling participants. The primary end point was self-reported late (≥ 5 years after cancer diagnosis) VTE. Rate ratios (RRs) were estimated with multivariable piecewise exponential models. Results Late VTE incidence among survivors and siblings was 1.1 and 0.5 events per 1,000 person-years, respectively (RR, 2.2; 95% CI, 1.7 to 2.8), with 2.5 excess events per 100 survivors over 35 years. Among survivors, risk factors for VTE were female sex (RR, 1.3; 95% CI, 1.1 to 1.6), cisplatin (reference none; 1 to 199 mg/m²: RR, 3.0 [95% CI, 1.4 to 6.5]; 200 to 399 mg/m²: RR, 1.9 [95% CI, 1.0 to 3.6]; ≥ 400 mg/m²: RR, 2.0 [95% CI, 1.2 to 3.3]), l-asparaginase (RR, 1.3; 95% CI, 1.0 to 1.7), obesity or underweight (reference body mass index [BMI] 18.5 to 24.9 kg/m²; BMI ≥ 30.0 kg/m²: RR, 1.6 [95% CI, 1.2 to 2.0]; BMI < 18.5 kg/m²: RR, 2.4 [95% CI, 1.7 to 3.4]), and late cancer recurrence or subsequent malignant neoplasm (RR, 4.6; 95% CI, 3.6 to 5.8). Among lower-extremity osteosarcoma survivors, limb salvage (reference amputation; RR, 3.1; 95% CI, 1.2 to 7.5) and cisplatin 200 to 399 or ≥ 400 mg/m² (reference none; RR, 4.0 [95% CI, 1.1 to 14.6] and 2.9 [95% CI, 1.1 to 8.0], respectively) were independently associated with late VTE. VTE was associated with increased risk for nonexternal cause late mortality (RR, 1.9; 95% CI, 1.6 to 2.3). Conclusion Childhood cancer survivors are at increased risk for VTE across their lifespan and a diagnosis of VTE increases mortality risk. Interventions that target potentially modifiable comorbidities, such as obesity, warrant consideration, with prophylaxis for high-risk survivors, including those treated with cisplatin and limb-sparing approaches.