Chest wall or pleural-based tumours represent a heterogeneous group of lesions that are infrequent in children and infants; however, a large proportion of these lesions are malignant in nature. Categorising them on the basis of primary versus secondary, site of origin (osseous and cartilage, or soft tissue) and tissue composition may assist in narrowing the differential diagnosis. We present a case of a 7-year-old boy with a progressive history of dyspnoea. The initial chest radiograph (CXR) demonstrated complete opacification of the left hemithorax with no air bronchograms. This was associated with the cut-off of the left main bronchus and mediastinal shift to the right. The post-contrast computed tomography (CT) of the chest showed multiple left-sided enhancing pleural-based masses with collapse of the left lung. These lesions were locally invasive as demonstrated by the intra and extra-thoracic extension. There were no associated erosions of the adjacent ribs or intra-tumoural calcifications. Based on the imaging findings, the diagnosis of extra-skeletal Ewing sarcoma (ES-EWS) of the chest wall was made with a differential diagnosis of rhabdomyosarcoma. A core biopsy was performed of the pleural-based mass, and histology with immunohistochemistry confirmed the diagnosis of a malignant small round blue cell tumour; subtype Ewing sarcoma family tumour (ESFT). The child was subsequently commenced on chemotherapy. The diagnosis of ES-EWS should be considered when a child or adolescent presents with an ill-defined, eccentric, chest wall mass in the absence of a lesion with a primary osseous origin. Imaging plays a key role in tumour staging, therapeutic planning and follow-up of patients.