Introduction. Pneumothorax is a life-threatening condition which may be the first manifestation of a tumor in the chest cavity in children.Material and methods. The article describes a clinical case of a two-year-old patient with spontaneous pneumothorax.Results. By literature data, pleuropulmonary blastoma is the most common malignant tumor of the thoracic cavity in young children. It is a thin-walled single or multi-cavity formation located on the lung periphery. It has a high risk of metastases, relapses as well as a tendency to higher malignancy degree. Therefore, the overall survival of patients is significantly reduced in case of late tumor detection. It is known that at early stages the structure of pleuropulmonary blastoma is similar to that of the bullous transformation in lungs, and in most cases it does not have characteristic clinical manifestations; therefore, early diagnostics of the neoplasm in case of pneumothorax depends on surgeon’s oncological alertness and on the tactics chosen by him/her to treat the complication. The performed videothoracoscopic resection of the cystic formation in the left lung did not only helped to achieve aerostasis within the short time, but it also helped to find out the cause of the complication: it was a rare malignant tumor of the lung - pleuropulmonary blastoma.Conclusion. The tumor process at the preoperative stage is difficult to suspect in children because in most cases there are no specific clinical symptoms. So, an active surgical tactics in treating cystic lung formations in patients with pneumothorax allows not only to eliminate the complication, but also to identify a malignant neoplasm at the initial stage.