text: The impact of COVID 19 lockdown on child and adolescent mental health systematic review COVID 19 was declared a pandemic in March 2020 resulting in many countries worldwide calling for lockdowns This study aimed to review the existing literature on the effects of the lockdown measures established as a response to the COVID 19 pandemic on the mental health of children and adolescents Embase Ovid Global Health PsycINFO Web of Science and pre print databases were searched in this PRISMA compliant systematic review PROSPERO CRD42021225604 We included individual studies reporting on a wide range of mental health outcomes including risk and protective factors conducted in children and adolescents aged 19 years exposed to COVID 19 lockdown Data extraction and quality appraisal were conducted by independent researchers and results were synthesised by core themes 61 articles with 54 999 children and adolescents were included mean age 11 3 years 49 7 female Anxiety symptoms and depression symptoms were common in the included studies and ranged 1 8 49 5 and 2 2 63 8 respectively Irritability range 16 7 73 2 and anger range 30 0 51 3 were also frequently reported by children and adolescents Special needs and the presence of mental disorders before the lockdown alongside excessive media exposure were significant risk factors for anxiety Parent child communication was protective for anxiety and depression The COVID 19 lockdown has resulted in psychological distress and highlighted vulnerable groups such as those with previous or current mental health difficulties Supporting the mental health needs of children and adolescents at risk is key Clinical guidelines to alleviate the negative effects of COVID 19 lockdown and public health strategies to support this population need to be developed 