We report a case of a splenic inflammatory pseudotumor (myofibroblastic tumor) in a 43-year-old man with a 5-year history of chronic bronchitis and sleep apnea syndrome. The patient was hospitalized because of a screen-detected splenic mass lesion. His sputum cultures revealed Mycobacterium avium complexes on only one occasion. Imaging studies revealed a 7 cm solitary tumorous lesion, and differential diagnoses of splenic hamartoma, hemangioma, lymphoma, and angiosarcoma were obtained from the radiologist. A splenectomy followed by pathological investigations was performed. By histology, the lesion contained fibroblastic or myofibroblastic spindle cell proliferations, accompanied by variable degrees of inflammatory cell infiltration. Ziehl-Neelsen staining did not reveal acid-fast bacteria. Immunohistochemically, the fibroblastic or myofibroblastic spindle cells were positive for vimentin, human smooth muscle actin, and muscle actin, but negative for desmin, CD8, CD21, CD23, CD35, p80, Epstein-Barr virus LMP, and human herpesvirus type 8. The infiltrating lymphoid cells demonstrated a nonneoplastic pattern. The results of in situ hybridization for Epstein-Barr virus encoded RNA were negative. The postoperative course was uneventful and he has had no recurrence in 22 months. His sleep apnea syndrome and chronic bronchitis have resolved spontaneously since the splenectomy. [J Clin Exp Hematopathol 47(2) : 83-88, 2007]