It has been suggested that lung cancer is frequently associated with polymyositis/dermatomyositis (PM/DM). The purpose of this study was to describe the clinical features of primary lung cancer associated with PM/DM. We first describe the clinical features of two cases treated in our hospital, and then provide a review of the literature. Finally, 24 patients (five females and 19 males) with primary lung cancer associated with PM/DM are retrospectively evaluated. Histological types of lung cancer were as follows: small cell lung cancer (n = 7), squamous cell carcinoma (n = 5), adenocarcinoma (n = 2), others (n = 5), and unknown (4). The onset of PM/DM is frequently observed before the detection of lung cancer. This is the first report to describe the clinical features of lung cancer associated with PM/DM.