Primary malignant chondromatoid tumors of the lungs are rare. We report on a case of a 49-year-old woman who presented with a round focus in the upper lobe of the left lung. The performed biopsy showed features of a leiomyosarcoma. After chemotherapy and consecutive tumor resection, the histologic investigation of the entire tumor mass revealed a dedifferentiated chondrosarcoma. Careful clinical and radiologic examinations showed no evidence of further pulmonary and extra-pulmonary tumor lesions. The final diagnosis of a primary dedifferentiated chondrosarcoma of the lung was based on the morphologic criteria and review of the literature. The differential diagnosis of malignant hamartoma was discussed. Follow-up investigation after 2.5 years showed no evidence of another primary tumor site.