The authors present the case of a 67 year-old man with a 50-pack-year history of cigarette smoking. He had been in the navy for 30 years where he was exposed to asbestos fibbers.He had been asymptomatic until the age of 62, when he started to experience increasing exertional dyspnoea. One year later he had an episode of fever, productive cough and myalgias. Digital clubbing was noticed and bibasilar crackles were present on chest auscultation.Thoracic CT scan obtained at that time, were compatible with Usual Interstitial Pneumonia and bronchoalveolar lavage excluded other diseases. Pulmonary function studies: restriction and decreased DLco.Deflazacort, acetylcysteine and azathioprine were administered. Azathioprine was then switched to cyclophosphamide because of clinical and functional deterioration. Two years later he began Interferon Gamma 1b, with clinical and functional improvement lasting one year.He was then diagnosed Polymyositis and received Immunoglobulin.Twelve months later he was admitted to the hospital with intermittent fever, non productive cough, worsening exertional dyspnoea and myalgias. The Thoracic scan showed honeycombing and bronchiectasis. In the left inferior lobe there was a peripheral nodule. The patient was submitted to a Thansthoracic Needle Biopsy, the tissue immunocytochemistry pattern revealed Small Cell Lung Cancer. In the staging procedures there were positive mediastinal and hilar nodes and multiple hepatic metastases.Only one administration of chemotherapy was performed with carboplatinum and etoposide, without response. Unfortunately the patient died a fortnight later.Polymyositis has been associated with a variety of malignancies, in this case, the patient developed pulmonary fibrosis previously to the diagnosis of Polymyositis, and only several years later Small Cell Lung cancer was diagnosed.