Pulmonary hyalinizing granulomas are distinct fibrosing lesions of lung, having central whorled deposits of lamellar collagen. Twenty-four cases of this unusual pulmonary lesion are reported herein. Hyalinizing granulomas occur in middle-aged persons and are frequently mistaken for metastatic carcinoma radiographically. More than half of the patients had autoimmune phenomena or previous exposures to mycobacterial or fungal antigens. Four patients had sclerosing mediastinitis develop. A progressive debilitating clinical course was related to increasing dyspnea and bilateral disease on chest radiographs. A discussion of the histogenesis and histologic differential diagnosis is presented.