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 radio- graphically. 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.