The authors discuss a case of malignant small round cell tumor of the thoracopulmonary region (Askin tumor) in which the initial pathological diagnosis was "sarcoma". Only a review of the histological specimens and the clinical features and evolution revealed the correct diagnosis of "Askin tumor". A 15 year old girl with fever, dyspnoea, cough underwent thoracentesis, which revealed hemothorax. At surgery, a large mass not involving the lung, with pleural thickening, was found in the left hemithorax and excised, without rib resection. No metastasis was observed at that time. Histological findings revealed features of malignant small round cell tumors, with occasional pseudo-rosettes. Chemotherapy was performed. 16 months after clinical presentation the girl died with abdomino-thoracic metastatic disease.