Background: Sarcomatoid carcinoma (SARC) of the lung is a very rare and aggressive type of non-small cell lung cancer. It belongs to a group of poorly differentiated carcinomas with partial sarcomatoid differentiation or with a direct sarcoma component. Characteristic findings include a large tumor with an invasive tendency, early recurrence and systemic metastases. Case: The authors present a case of SARC in the 77-year- old patient. Preoperative staging confirmed sarcomatoid carcinoma of the lower lobe of the left lung without generalization on PET/ CT. However, an infiltration of more than 2/ 3 of the diaphragm was ascertained. A resection was performed – a left lower lobectomy with resection of the diaphragm and its replacement by a muscle flap made from the latissimus dorsi muscle with vascular pedicle. Histological findings confirmed the diagnosis of sarcomatoid (pleomorphic) carcinoma pT3N0M0. The patient underwent adjuvant chemotherapy; recurrence and systemic dissemination of the disease occurred after 20 months; the patient died 21 months after the surgery.