A number of benign clinical conditions of the lung may simulate carcinoma. Pulmonary pseudotumor, which falls into this category, may present as a mass lesion or rarely as an infiltrate. This paper describes six patients with pulmonary pseudotumor, their surgical treatment and, for the first time, a postoperative follow-up ranging from 1 to 10 years. Histories of heavy cigarette smoking were obtained in four. Discrete masses on x-ray films were present in five, and one had localized infiltrates. Lobectomy was performed in two and partial mass resection or removal of tissue for biopsy in four. In this latter group, postoperative x-ray films from 1 to 10 years later showed complete disappearance of the lesions. No subsequent malignant lesion developed, and there was no early or late mortality. This unique experience documents for the first time the natural course of pulmonary pseudotumor. On the basis of this and isolated reports in the literature, pseudotumor must be carefully differentiated from carcinoma. Once diagnosed, as minimal lung resection as possible is indicated.