Objectives. Compared with the general population, childhood cancer survivors (CCS) could be at greater risk of psychological distress following the emergence of the COVID-19 pandemic. This cross-sectional study assessed the psychological consequences of COVID-19 on the mental health of CCS. Methods. In December 2020, we interviewed through an online self-report questionnaire 580 5-year CCS participating in the French Childhood Cancer Survivor Study (FCCSS) cohort. We first compared the mental health score of CCS with that observed in the French general population of the same age and gender. Subsequently, combining clinical and patient-reported outcomes, we studied predictors of the mental health score of CCS. Results. External comparisons revealed that the mental health score of CCS was similar to that observed in the general population. Among CCS, almost 42% stated that their psychological state had been worse during the lockdown. Predictors of poorer mental health included, among others, female gender, reporting a change of his/her occupational situation, having a relative who had been hospitalized or had died following COVID-19, and a greater perceived infection risk. Conclusion. Given the pre-existing vulnerability of some CCS to mental distress, the additional psychological consequences of COVID-19 in vulnerable survivors should receive attention from health care providers.