Hypothesis: To establish the hypothesis that the clinical and audiometric thresholds prompting testing for retrocochlear disease should be liberal. The question, “What are appropriate clinical thresholds that would trigger further testing for retrocochlear lesions?” has a very long history. Harvey Cushing, MD, first identified unilateral hearing loss and tinnitus as cardinal symptoms of acoustic neuromas in his classic 1917 monograph. Since then, the evaluation of asymmetric sensorineural hearing loss (ASNHL) (and other associated symptoms) has been the central focus regarding the search for retrocochlear disease. Long before the advent of magnetic resonance imaging (MRI), various audiometric tests were developed for their usefulness in selecting which patients with ASNHL should be subjected to more invasive testing in the search for retrocochlear causes of hearing loss (HL) such as an acoustic neuroma or other cerebellopontine angle (CPA) lesions. In that era (prior to the late 1970s), the radiological testing was quite invasive and carried potential for significant complications. Finding small tumors with these techniques was challenging. Typically, patients in the mid1900s could count on having mediumto large-size tumors at time of diagnosis. Surgical treatment doomed them to unilateral deafness and likely permanent ipsilateral facial paralysis. The clinical availability of computed axial tomography (CT) scanning in the late 1970s advanced our ability to diagnose smaller tumors in a less invasive way. Auditory brainstem response (ABR) testing came into clinical practice in the early 1980s and was thought to be a highly useful screening tool for ASNHL. The gold standard for diagnosis of retrocochlear lesions was established with the advent of gadoliniumenhanced MRI in the late 1980s. It is now routine to find small tumors in which hearing and facial nerve preservation are realistic treatment goals. Whereas, in the past, audiometric criteria helped select patients appropriate for more dangerous testing, the current discussion regarding advanced diagnostic testing of patients with ASNHL centers on financial costs and the prudent use of limited health care resources. Discussion of what degree of HL should be considered asymmetric is undertaken. Once the clinical threshold is met, MRI should be the test of choice to screen for retrocochlear disease. Furthermore, economic analysis of the algorithm this article recommends will be presented. Fundamental to the discussion of audiometric criteria for evaluating ASNHL is a definition of what constitutes asymmetric hearing. First, the interaural difference in puretone hearing should be greater than what can be expected from testretest variability. Audiometric testing is performed in 5-dB steps, and studies have indicated the range for test-retest variability in behavioral audiometric testing is 10 dB. Hence, a difference of 15 dB, in a single frequency, would be the lowest level of asymmetry feasible given the aforementioned limitation. Next, would asymmetry in a single frequency be sufficient to trigger heightened suspicion for retrocochlear disease? There is no literature to support a particular number of frequencies that constitutes a significant asymmetry. Whereas single-frequency asymmetries are exceedingly common in individuals without disease, most articles addressing audiometric criteria for retrocochlear lesion testing cite asymmetry in 2 frequencies as the lowest threshold. Therefore, with regard to pure-tone sensorineural thresholds, an asymmetry of 15 dB in 2 audiometric frequencies (in the same ear) would be the lowest reasonable threshold to recommend further evaluation. Next, one must consider speech discrimination scores (SDSs). The literature strongly suggests that asymmetry in SDSs is highly suspicious for retrocochlear disease, particularly when found in combinaRoberto A. Cueva, MD