Necrotizing infections of the head and neck are rare conditions in our hospital. Clinical and microbiological characteristics of three consecutive cases treated in Haukeland University Hospital in western Norway in the year 2010 are described. Two cases of Lemierre’s syndrome and one case with a descending necrotizing mediastinitis (DNM) were diagnosed. All three cases were treated with broad spectrum antibiotics and in two cases surgery was possible. Hyperbaric oxygen treatment (HBOT) with intensive care facilities became recently available at our hospital, and this treatment was used in all these patients regardless of surgery. In one case we describe the use of HBOT on the basis of strong clinical suspicion of anaerobic infection only. Bacterial identification by partial sequencing of the 16SrDNA gene proved to be a useful supplement to conventional culture techniques. All the cases all demonstrated a significant clinical improvement after introduction of HBOT. When HBOT is available, it should be considered as adjunctive treatment in extensive infections with anaerobes.