Reactive pseudosarcomatous lesions of soft tissues are uncommon and challenging entities. They mimic sarcomas because of the clinical history of rapid growth and spindle cell proliferation. Some of these lesions are characterized by new bone or osteoid formation. In this report the clinical, histological, histochemical and immunohistochemical features of 13 cases of these reactive fibroproliferative lesions composed of an ossifying fasciitis, an aneurysmal bone cyst of soft tissue, 1 myositis ossificans, 3 proliferative fasciitis and 7 nodular fasciitis cases with follow ups between 8 months to 14 years, were analyzed. Some of those cases had a history of trauma. These lesions were collagen rich in Masson’s trichrome. Immunohistochemically; smooth muscle actin and vimentin were strongly positive. Our case of ossifying fasciitis is the 13th cases and aneurysmal bone cyst of soft tissue case is the 15th cases of the literature. As a result; clinical and morphological features of those entities were found similar to each other. Finally a unifying concept of fibroblastic and myofibroblastic proliferation in response to trauma, genetic and/or an unknown factor are proposed.

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