Inflammatory sarcomatoid carcinoma is an aggressive tumor with an unusually benign appearance. We report the case of a 65-year-old man with a history of inoperable poorly differentiated carcinoma of the right lung, for which he had received chemoradiotherapy. A new solitary mass was discovered 4 years later in the left lung on surveillance computed tomography. The patient underwent thoracotomy with a wedge biopsy on which frozen section was performed. The nodule was vaguely granulomatous and associated with a mixed inflammatory infiltrate and a deceptively bland spindle cell proliferation. Results of immunoperoxidase studies, however, showed that the nodule contained neoplastic cells with an epithelial phenotype that were invading the pulmonary vessels. These are features of the rare inflammatory sarcomatoid carcinoma. In contrast to sarcomatoid carcinomas, this case highlights the deceptively benign appearance of inflammatory sarcomatoid carcinoma. This leads us to concur with the recommendation to exercise caution when attempting the diagnosis of apparently benign lesions on intraoperative frozen section in patients with high clinical suspicion of malignancy.