Lung cancer during pregnancy is a rare situation which is being increasingly reported during the past two decades due to a rising trend of cigarette smoking among young women and the tendency to delay pregnancy to a later age in life. We describe the case of a 32-year-old woman with primary pulmonary sarcoma, diagnosed at 31st week of pregnancy. X-ray chest and thoracic magnetic resonance imaging revealed a 9 x 6 cm mass in the left mediastinum, with tracheal shift, and pleural effusion. Biopsy performed during broncoscopy, was reported as mesenchymal tumour. She delivered a baby by Caesarean section at the 32nd week of gestation due to the development of superior vena cava syndrome. A skin biopsy taken 3 weeks later from the nodular lesion at the periumblical region was reported as a tumour metastasis. She received radiotherapy for 10 days, but died in the intensive care unit. Malignancies, even those as uncommon as a pulmonary sarcoma, should be considered in the differential diagnosis of pleural effusion during pregnancy.