CASE PRESENTATION: A 9-month-old girl was admitted in the pediatric intensive care unit (PICU) for hypoxemia and severe wheezing of one week duration. Her symptoms responded poorly to therapy with bronchodilators and racemic epinephrine. A history of fever, rhinorrhea, dysphagia, eczema and stridor were not reported. Upon transfer to the PICU, the child received systemic steroids, diuretics, anti-reflux medications; supplemental oxygen along with bronchodilator therapy was administered continuously. The patient had experienced wheezing the very first time at two months of age; she developed right upper lobe pneumonia due to aspiration from acetaminophen administration following vaccination. Since then, the child experienced recurrent episodes of wheezing on a monthly basis which appeared to be triggered by a viral like illness. She was treated with systemic steroids every two months. Therapy with inhaled steroids was started at the age of seven months with mild improvement. Review of ancillary studies at the time of admission was mostly unremarkable with normal complete cell count and serum electrolytes. A venous blood gas at the time of transfer to the PICU was notable for respiratory acidosis with ph 7.17 and a pCO2 65 torr. A chest radiograph (CXR) revealed a nodular opacity over the superior mediastinum on the right side, which could represent thymus but had an unusual counter. A CXR was repeated the following day which revealed less prominence of the previously seen nodular opacity; however, a repeat film after three days revealed persistence of the radiographic abnormality. A computed tomography scan revealed a fluid density mediastinal mass centered beneath the carina and compressing the bronchus intermedius as well as the left main stem bronchus. The patient underwent surgical resection of a large cyst noted at the sub carinal region and has remained asymptomatic ever since.