Cardiac catheterization (CC) has largely improved the diagnosis and treatment of congenital heart disease in children over the last decades, but it leads to exposure to low doses of Xrays. Children have a greater radiation sensitivity, however, little is known about the long-term radiation associated cancer risks. Objective: This study aims to assess the risk of lymphohematopoietic malignancies among children diagnosed and/or treated with CC. Methods: The COCCINELLE cohort includes children from 15 French paediatric cardiology departments who underwent a first CC between 2000—2013, before 16 years old. The cohort was linked with national registries to identify cancer cases and collect information on predisposing factors to cancer (PF). Individual cumulative doses to active bone marrow (ABM) were calculated with the PCXMC software, based on detailed dosimetric information retrieved from reports of 1,139 CC procedures. Standardised incidence ratios (SIRs) and relative risks (RR) of haematological malignancies associated with the 2-year lagged ABM dose were calculated. Results/Expected results: The cohort included 17,104 children, followed 6.5 years on average. 22,227 CC procedures were collected, with a mean individual ABM cumulative dose of 3.0 mGy. 38 lympho-hematopoietic malignancies were counted (23 lymphoma and 15 leukemia). A significant excess of cancer incidence was observed (SIR = 3.8 [95% confidence interval 2.9; 4.9]), which wasn’t anymore observed after excluding patients with PF (SIR = 1.3 [0.6;2.7]). The ABM dose wasn’t significantly associated with the risk of lympho-hematopoietic malignancies (RR/mGy = 1.00 [0.88; 1.10]) or lymphoma (RR/mGy = 1.03 [0.90; 1.14]) after adjustment for attained age, gender and PF. Conclusion/Perspectives: No significant increase of cancer incidence was observed after excluding patients with PF and no dose-response relationship was observed between the risk of lympho-hematopoietic malignancies or lymphoma and cumulative ABM dose arising from CC procedure. The extension of the COCCINELLE study and the European Harmonic project will help to better assess health effects of CC exposure during childhood.