The spectrum of diseases diagnosed and the protocol used in the investigation of 200 consecutive patients with unilateral sensorineural hearing loss (SNHL) is presented. The diagnostic tests found most useful in defining the site of the lesion were a combination of a well-masked pure tone audiogram, speech discrimination score (SDS), acoustic reflex test (ART), and a vestibular evaluation using photoelectric nystagmography (PENG) and the Torok Monothermal Differential Caloric Test. With this protocol, the site of the lesion was correctly defined in 94% of patients with unilateral progressive SNHL. Laboratory and radiological studies confirmed a variety of lesions other than acoustic tumors. It is, therefore, felt that the primary objective of investigations should be to define the site of the lesion rather than aim to diagnose a specific disease entity.