A 73-year-old female with a past medical history of hystero-oophorectomy for uterine cancer at 60 years of age, who had never smoked, was examined in our department (Respiratory Medicine and Infection Control, Tokai University Hachioji Hospital, Tokyo, Japan) on November 12, 2012 after abnormal chest shadows were observed during a health check-up with a radiographer. The patient had no fever or cough, and no particular clinical manifestations were observed. Additionally, no superficial lymph nodes were palpable, and no skin rashes were noted. Chest radiography and computed tomography (CT) revealed infiltrative shadows primarily in the left pulmonary hilum, and small nodular shadows in both the right and left lung fields (Figs. 1 and 2). The blood examination and tumor marker results were within normal limits (CEA 2.0 ng/mL, CYFRA 1.1 ng/mL, RProGRP 31.6 pg/mL, NSE 8.7 ng/mL, sIL-2R 327 U/mL and KL-6 410 IU/mL); the interferon-gamma release assay for active tuberculosis (IGRA: T-SPOT.TB) was negative, and neither sputum cultures or cytology yielded any significant findings. Two weeks following the first relevant examination (FRE), a transbronchial lung biopsy (TBLB) was performed on the patient on November 26, 2012, who was admitted to the Tokai University Hachioji Hospital overnight. Histopathological assessment of the biopsy tissue revealed nonspecific organized tissue with no evidence of malignancy. No clinical manifestations were observed during that time; however, a definitive diagnosis was deemed necessary, and after consulting with the patient and obtaining consent, video-assisted thoracic surgery (VATS) and excision of the right upper nodule was performed on December 18, 2012, three weeks after the TBLB, for which the patient was admitted until December 28, 2012. Histological evaluation of the frozen material demonstrated the presence of an organizing pneumonia with no malignancy. A detailed pathological evaluation of fixed tissue led to the preliminary diagnosis of an IgG4-related, solitary, fibrous IMT, which required further immunohistochemical investigation. The immunostaining revealed that the nodule was vimentin-positive, strongly alpha-SMA-positive, CD34-negative, CD68-positive, Congo-red-negative, ALK-negative and IgG4-negative (Fig. 3). No evidence of malignancy, including evidence of cancer or spindle-cell carcinoma, was detected. The macroscopic findings showed a clearly demarcated mass. Based on the above findings, a final diagnosis of IMT was made. As there were no clinical manifestations, we consulted with the patient and decided to carefully follow her course. The chronic inflammation in the ALK-negative tissue was considered to be a chronic respiratory tract inflammation at that time. Clarithromycin was administered as a long-term macrolide antibiotic therapy, three months following the FRE, as we expected it would be effective in controlling the inflammation. The chest shadows slowly resolved on follow-up imaging examinations, performed every two months. The chest shadows had almost completely disappeared on the images obtained eight months following clarithromycin therapy (Figs. 1 and 2). Clarithromycin therapy was performed for ten months in total, and during this time there were no clinical manifestations and no impairments to the patient's everyday life. The patient has experienced no relapses, and appears to have followed a favorable course almost one year following the FRE.