Auditory neuropathy was once thought to be rare but it may be quite common and account for up to 10% of childhood cases of hearing loss, and can also be seen in older children and adults. It is an unusual cause of hearing loss. The understanding of how it occurs is still changing and is a source of some controversy amongst hearing specialists, as is its diagnosis and treatment. The most common progressive and severe hearing losses involve hair cell failure within the cochlea while leaving the auditory nerve intact and working well. This is why a cochlear implant usually works so well for most profound hearing losses. It stimulates a nerve which is still functioning. In Auditory Neuropathy Spectrum Disorder (ANSD) some of the hair cells (or at least the outer hair cells) may be functioning well but inner hair cells and/or the junction with the auditory nerve (the synapse) along with the auditory nerve itself seems to have failed. ANSD seems to occur in several clusters of patients. One cluster involves infants who are born preterm and spend some time in the neonatal intensive care. They may have been affected by some degree of birth trauma (hypoxia), high levels of jaundice and exposure to a variety of medications during their treatment. A second group generally develops later onset symptoms during childhood, adolescence or early adulthood. This group (the minority) often have associated neurological disorders with neuropathy affecting other parts of the body. Disorders such as Charcot- Marie-Tooth disease fit this category. Genetic defects with failure of the otoferlin gene, which is required for normal inner hair cell function, may also be underlying factors. As one can imagine, the diagnosis of such a variable and complex condition requires several sophisticated hearing test. This involves an audiogram (and speech perception test in older children or adults), otoacoustic emission studies (a test of outer hair cell function) and an auditory brain stem response test (ABR). The classical test results in ANSD are a variable degree of hearing loss on the audiogram, but poor speech discrimination, particularly in background noise; poor or absent ABR wave forms and intact otoacoustic emission. The problem with ANSD is that the outcomes of children and adults with the disorder is highly variable. The long term outcomes range from normal hearing, speech and language development, to such disordered hearing that a cochlear implant is considered. The response to hearing aids and cochlear implantation is also highly variable. At this stage of our understanding, patients with disorders limited to the cochlea (hair cell failure) may have good outcomes, while those involving poor auditory nerve function have outcomes which are more varied and difficult to predict. Much work is being done in furthering the understanding and diagnosis of ANSD as well as more strongly predicting the outcomes of treatments.