Inflammatory myofibroblastic tumor, also referred to as inflammatory fibrosarcoma, is a rare tumor composed of myofibroblastic spindle cells of uncertain etiology and disputed nosology. We report a case of inflammatory myofibroblastic tumor of the omentum with involvement of the bone marrow in an 18-year-old man. Histologic and immunohistochemical studies of the abdominal mass and bone marrow were consistent with inflammatory myofibroblastic tumor. Additionally, fluorescence in situ hybridization using a probe specific for the ALK gene showed disruption of the gene. The literature is reviewed with emphasis on the ability of inflammatory myofibroblastic tumor to recur, metastasize, and cause mortality.