Background: We aimed to clarify the surgical management of ectopic cervical thymus (ECT) in children. Methods: Case report and systematic review of the literature. Results: We report a case of ECT in a 10-year old girl initially misdiagnosed as branchial cyst. A systematic review of the literature (1997-2018) identified 143 paediatric patients (150 ECT) diagnosed as follows: 10 incidentally at autopsy, 107 after complete surgical excision, 33 after needle/ incisional biopsy/ imaging only. There were no reports of malignancy. Conclusions: ECT is a benign and relatively rare condition in children. ECT can be the only active thymus and careful consideration should be taken prior to its excision in young children. We recommend that ECT should be considered in the differential diagnosis of lateral neck masses in children. In cases where the exact aetiology is unclear investigation with an MRI scan of neck and thorax to avoid inappropriate surgical intervention.