Cervical necrotizing fasciitis is a rare, rapidly progressive, severe bacterial infection of the soft tissues of the neck. Uncommonly, it may descend into the mediastinum. We describe a case of descending necrotizing mediastinitis in a young man, where there was diagnostic confusion and delay, with an eventual fatal outcome. A steroid injection for neck pain is thought to be the source of infection. In this case, the signs of mediastinitis were initially masked, and the diagnosis delayed until cardiopulmonary arrest occurred. Early recognition with a low threshold for computed tomography (CT) scanning is essential. Aggressive multidisciplinary therapy with mediastinal drainage is mandatory.