We reviewed 223 localized fibrous tumors of the pleura and divided them histologically into 141 benign and 82 malignant neoplasms. The criteria used for a judgement of malignancy were high cellularity and mitotic activity (more than four mitotic figures per 10 high-power fields), pleomorphism, hemorrhage, and necrosis. The tumors occurred equally in both sexes, most commonly in the sixth to seventh decades of life. Presenting symptoms included chest pain, dyspnea, and cough; they were observed in three-fourths of patients with a malignant tumor. One in every four of these patients had hypoglycemia, clubbed digits, or pleural effusion. Two-thirds of the tumors were attached to visceral pleura, often by a pedicle. The rest arose from the parietal pleura of the chest wall, diaphragm, or mediastinum. Neoplasms in these atypical sites, together with fissural lesions and tumors "inverted" into peripheral lung, were more often malignant. Most neoplasms measured 5-10 cm and weighed 100-400 g. Microscopically, the "patternless pattern," or hemangiopericytic type, was seen in the majority of cases, and mixed patterns were seen in nearly 40% of tumors. Of the 169 tumors where follow-up was available, all of the benign and 45% of the malignant tumors were cured by simple excision. Patients surgically cured of a malignant neoplasm had pedunculated or well-circumscribed lesions. However, 55% of patients with malignant tumors succumbed to their disease secondary to invasion, recurrence, or metastasis. Resectability is the single most important indicator of clinical outcome. No tumor expressed epithelial differentiation, either immunohistochemically or ultrastructurally; therefore, we favor the term "localized fibrous tumor" of pleura instead of "localized mesothelioma."