Descending necrotizing mediastinitis (DNM) is a rare and life-threatening complication of deep neck space infection which occurs when infection spreads from the deep spaces of the neck, propagating within the soft tissue into the mediastinal spaces. The disease has a high mortality rate due to frequent delay in diagnosis and treatment. Computed Tomography (CT) is important in determining the level of infection, showing the presence and extension of fluid collections (with or without gas bubbles) and diffuse soft-tissue infiltration of the mediastinal fat, and indicating the best surgical approach and progress of treatment. Three cases of DNM evaluated with spiral CT from June 1999 to June 2001 are presented.