Inflammatory myofibroblastic tumor (IMT) or inflammatory pseudotumor was initially recognized in the lung, and somewhat later, a similar-appearing pathological process was reported in the liver. Presently, this tumor has been described in virtually all major organs and extrapulmonary sites with a few exceptions. It was thought initially that the IMT was nonneoplastic and represented an aberrant inflammatory response despite its gross and microscopic features of a spindle cell neoplasm. The inflammatory hypothesis about the pathogenesis has been more readily accommodated in the lung than in the extrapulmonary sites of involvement. Some cases, however, were accompanied by the constitutional symptoms and signs of an inflammatory process, which resolved in most cases after surgical resection. There were some pathological aspects of the IMT that seemingly contradicted its purely inflammatory nature, including its potential for local recurrence; development of multifocal, noncontiguous tumors; infiltrative local growth; vascular invasion; and malignant transformation. These pathological features seemed to support the hypothesis that the IMT is a neoplastic process, which has been augmented by reports that these tumors have clonal characteristics. Other studies have suggested that IMTs of the liver and spleen are associated with the Epstein-Barr virus. From the diagnostic perspective, there are several potential difficulties that the pathologist may encounter in the examination of one of these tumors. Just as it was true 60 years ago, the potential for a pathological diagnosis of one or another type of spindle cell sarcoma has not diminished with time. Because these tumors have a predilection for children, embryonal rhabdomyosarcoma is another diagnostic temptation when an IMT presents in the bladder or other hollow viscus. The IMT should probably be regarded as a soft tissue-mesenchymal tumor with an indeterminant or low malignant potential, which is a somewhat indefinite but realistic prognostic category.