A 53-year-old man was admitted to our department because of interstitial pneumonia found on chest computed tomography when he was given a diagnosis of amyopathic dermatomyositis. Bronchoalveolar lavage (BAL) fluid showed an increased total cell count and lymphocytosis. An acute exacerbation of interstitial pneumonia occurred just after the BAL. Although the administration of corticosteroid and immunosuppressant for the progressive interstitial pneumonia produced temporary improvement, left hemothorax suddenly occurred soon after initiating treatment. The hemothorax was improved by thoracic drainage alone, but the patient died due to progressive worsening of interstitial pneumonia. In this case, we could not clarify the etiological mechanism of the hemothorax, however, there was a possible link with amyopathic dermatomyositis-associated interstitial pneumonia.