Deafness affects ∼2 in 1000 children and is one of the most common congenital impairments. Permanent hearing loss can be treated by fitting hearing aids. More severe to profound deafness is an indication for cochlear implantation. Although newborn hearing screening programs have increased the identification of asymmetric hearing loss, parents and caregivers of children with single-sided deafness are often hesitant to pursue therapy for the deaf ear. Delayed intervention has consequences for recovery of hearing. It has long been reported that asymmetric hearing loss/single-sided deafness compromises speech and language development and educational outcomes in children. Recent studies in animal models of deafness and in children consistently show evidence of an "aural preference syndrome" in which singlesided deafness in early childhood reorganizes the developing auditory pathways toward the hearing ear, with weaker central representation of the deaf ear. Delayed therapy consequently compromises benefit for the deaf ear, with slow rates of improvement measured over time. Therefore, asymmetric hearing needs early identification and intervention. Providing early effective stimulation in both ears through appropriate fitting of auditory prostheses, including hearing aids and cochlear implants, within a sensitive period in development has a cardinal role for securing the function of the impaired ear and for restoring binaural/spatial hearing. The impacts of asymmetric hearing loss on the developing auditory system and on spoken language development have often been underestimated. Thus, the traditional minimalist approach to clinical management aimed at 1 functional ear should be modified on the basis of current evidence.Deafness is one of the most common congenital impairments. 1,2 Newborn hearing screening programs, implemented in many countries, have decreased the age at diagnosis of hearing loss. When hearing loss occurs in only 1 ear, the screening result may be overlooked or dismissed as unimportant, particularly when hearing in the opposite ear is normal (unilateral or single-sided deafness). The consequence will be a failure to intervene until long after major developmental effects have set in, which causes significant negative clinical implications. Screening programs will also miss children who acquire deafness in 1 ear from infection, trauma, or worsening of preexisting hearing loss. 3-6 Acquired unilateral deafness can go unidentified until educational, social, or other impairments push families and caregivers to seek medical consult. Because the prevalence of permanent unilateral hearing loss in neonates is reported to vary from 0.45 to 2.7 in 1000 7,8 In this State-of-the-Art Review, we present evidence from basic and applied neuroscience, audiology, and otology that points to the existence of an impairment of the central representation of the poorer hearing ear if developmental asymmetric hearing is left untreated for years. First, we review the current state of the problem as viewed in the clin...