Although there are three kinds of stupor in psychiatry, dissociative stupor is the most commonly recognized. In psychiatric clinics or emergency rooms, dissociative stupor is common, but in an oncology setting it is hardly known. Therefore, distinguishing dissociative stupor from consciousness disorder is occasionally difficult, especially in the advanced or terminal phase. We report an advanced lung cancer patient who presented dissociative stupor mimicking consciousness disorder. It is necessary to distinguish between consciousness disorder and dissociative stupor. In addition, consultation with a psychiatrist should be taken into consideration.