The teratoma is a germ tumour, which originates from multipotent germ cells. It consists of various types of tissue derived from embryonic layers (endoderm, mesoderm and ectoderm), which are not normally found in the affected organ. The embryonic cell layers can produce mature, benign teratomas, with well differentiated tissues, or immature teratomas, potentially malignant, when the tumour is composed of undifferentiated tissues. After gonads, the mediastinum is the most frequent location of teratomas in children. The authors present the case of a caucasian 14-month-old boy admitted for cough, shortness of breath and wheezing. Chest radiography showed an oval homogeneous opacity in the anterior mediastinum, occupying almost the entire right hemithorax. CT scan revealed a cystic tumour measuring 8.3/6.5 cm in size, with calcifications inside; all the mediastinal structures were deviated to the left. Serum alpha-fetoprotein had slightly elevated values, namely 9.17 mg/ml (normal<7), and the chorionic gonadotropin hormone level was normal (<0.1 IU/ml). Right thoracotomy with tumour removal was performed; the tumour had macroscopic aspect of teratoma. Microscopically, the diagnosis of cystic teratoma with immature and mature nervous tissue was confirmed. The child underwent subsequently chemotherapy. Finally, the evolution was favourable. Considering the symptoms of presentation, the authors believe that the mediastinal teratoma should be considered for differential diagnosis with other causes of dyspnea in infant and child, even if it is rare at this age.