A case of inflammatory pseudotumor of the lung in a 6-year-old boy is presented. The respiratory illness presented as a mycoplasma pneumonia and there had been a similar episode of mycoplasma pneumonia one and a half years previously. Computed tomography revealed a large, calcified right posterior mediastinal mass and exploratory thoracotomy revealed a large posterior mediastinal mass that had an endobronchial component and grew exophytically from the lung. The present case suggests that inflammatory pseudotumor of the lung can manifest as a mediastinal mass and could be associated with mycoplasma pneumonia infection.