30 children with Ewing's sarcoma, the most common malignant pelvic tumour in childhood, were analysed. The diagnosis of Ewing's sarcoma is relatively easy and can be established in most of the cases on plain radiography. The diagnostic radiographic features of the tumour are discussed. The two most important conditions in differential diagnosis are eosinophilic granuloma and the rare primary bone lymphoma. Osteomyelitis should rarely cause confusion unless the clinico-radiographic findings are not properly evaluated.