Objectives Admission of patients with necrotising otitis externa (NOE) has been rising steadily over the last five years and mortality and morbidity associated with the disease is high. Our objective is to assess the value of adjuvant hyperbaric oxygen therapy in patients with necrotising otitis externa. Design and setting A retrospective, observational, case-control study was conducted by examining patients’ records over a four-and-a-half-year period at two secondary care sites in the UK. The (Non-HBO) control group treated conventionally and the (HBO) group treated with additional adjuvant HBO in a multiple occupancy therapy chamber at the James Paget University Hospital. The primary outcome measure was death. Secondary outcomes measures were resolution of pain and recovery from otalgia, facial nerve palsy and other cranial nerve palsies. Results There were 10 patients in the HBO group and 20 in the non-HBO group; mean age was 82.3 years and 88.3 years respectively. The mortality rate was 30% in the HBO group compared to 55% in the non-HBO group. Patients tolerated HBO well, had greater resolution of pain (90% vs 64%) and resolution of facial nerve palsy (67% vs 31%) than the non-HBO group. Resolution of other cranial neuropathies was similar. Conclusion Our case series suggests that HBO is potentially a life-saving intervention. It also suggests that patients treated with HBO therapy for NOE appear to improve both in terms of pain and facial nerve palsies compared with conventional treatment and sets the precedent for a trial to formally compare the adjunctive intervention of HBO.