In a multicentre retrospective cohort study of children and adolescents hospitalized with COVID-19 or multisystem inflammatory syndrome in children (MIS-C), thrombotic events occurred in 9/426 patients (2.1%) with COVID-19 and 9/138 patients (6.5%) with MIS-C. In addition to MIS-C, risk factors for thrombosis in these patients included age ≥12 years, cancer and the presence of a central venous catheter. In those patients who developed thrombosis, the mortality was high (28%).