We describe a rare case of a 46-year-old Japanese man with dermatomyositis (DM) and interstitial lung disease who developed spontaneous pneumomediastinum and subcutaneous emphysema. Relatively mild myositis, mild elevation of CK values and the absence of anti-Jo-1 antibody were observed and the case was similar to amyopathic DM. Treatment of this patient with oral prednisolone and cyclosporin A (CsA) was effective for the myositis and interstitial lung disease. The administration of CsA enabled rapid tapering of the dose of prednisolone without aggravating the disease. Pneumomediastinum and subcutaneous emphysema disappeared 5 months later without recurrence. The serum levels of KL-6 were monitored every 2 weeks to help determine whether this may have contributed to the recurrence of interstitial pneumonitis. This is a rare case of pneumomediastinum in a patient with DM.