A muscle biopsy established the diagnosis of dermatomyositis in a 22-year-old woman with normal muscle enzyme levels, 18 months after she presented with constitutional symptoms, a rash and polyarthritis. Her subsequent course was complicated by cutaneous ulcers with histological changes suggesting vasculitis, interstitial pulmonary involvement and recurrent pneumomediastinum, the latter being recently reported in 2 other cases of dermatomyositis. Cutaneous vasculitis has been present in all cases and it is suggested that the pneumomediastinum may be due to pulmonary vasculitis.