This is the report of a patient with a large cervico-mediastinal tumor that regressed spontaneously 4 weeks after its discovery. The 7-year-old boy was admitted with cough and fever. Chest x-ray showed a large mediastinal mass which displaced the trachea to the right. The following investigations: esophagram, computed tomography (CT) and magnetic resonance imaging (MRI) revealed the large, longitudinal mass to be in the posterior mediastinum. The mass was well delineated and consisted of solid and cystic components, extending from the hypopharynx, para- and retroesophageal, until below the bifurcation of the trachea. The esophagus and the trachea, were pushed to the right and ventrally, but no esophageal obstruction was seen. A more precise diagnosis was not possible and surgical resection was scheduled 3 weeks later. The CT 24h prior to the operation showed a marked decrease of the tumor. The operation was canceled and an esophagoscopy performed: the suspected enteric duplication was not found, but a white-yellow polyp-like lesion 2,5/1 cm in the middle of the esophagus. Biopsy of the tumor showed a lesion with similar histologic appearance as a non Langerhans-cell-histiocytosis. Eight months later the mass had disappeared on MRI. The patient was controlled 3 6/12 years after hospital discharge: he had no complains, chest x-ray was normal. To wait and simply closely follow the non malignant and otherwise not precisely defined tumor may be sometimes the correct „therapy„.