A 7-month old girl with the complaints of crying, cyanosis and breathing rapidly was brought to a hospital by her family. After taking nebulised salbutamol, the symptoms relieved. However, the symptoms reoccurred despite appropriate acute bronchiolitis treatment. She was hospitalized due to massive right thoracic infiltration in the chest x-ray. During evaluation, thoracal ultrasound showed a suspicious solid mass at the posterior mediastinum. Thorax computerised tomography revealed a right hemithoracal and posterior mediastinal gross solid mass. As the staging procedure, bone marrow aspiratıons were done which resulted in normal findings. The trucut biopsy of the thoracal mass resulted as small round blue malignant tumor cells consistent with peripheral neuroectodermal tumor/ewing sarcoma whıch was very rare in this age group.