Introduction: Unilateral and bilateral sudden sensorineural hearing loss represent different disease entities. The unilateral condition is more common and predominantly idiopathic, and up to 65 per cent of patients spontaneously recover hearing. Conversely, the bilateral condition is rare, mostly associated with serious systemic conditions, and has a higher prevalence of morbidity and mortality. Methods: A literature search using the PubMed database was conducted using the MeSH terms 'sudden', 'bilateral' and 'sensorineural hearing loss'. Results: One hundred and three reported cases of bilateral sudden sensorineural hearing loss were identified. The condition is most often associated with toxic, autoimmune, neoplastic and vascular conditions. A younger age of onset, with a bimodal age distribution, was seen for bilateral sudden sensorineural hearing loss, compared with the unilateral condition. Patients with the bilateral condition had more profound hearing loss, with poorer recovery and a 35 per cent mortality rate. Vestibular symptoms were also less common than in the unilateral condition. Conclusion: The presentation of bilateral sudden onset sensorineural hearing loss is a medical emergency requiring thorough and urgent investigation to exclude life-threatening and reversible conditions. Copyright © JLO (1984) Limited 2013.