Tinnitus can be perceived in one or both ears or in the head. It is usually described as a ringing noise, but in some patients it takes the form of a buzzing, hissing, humming, or whistling sound, or as ticking, clicking, roaring, "crickets", tunes, songs, or beeping. It has also been described as a "whooshing" sound, as of wind or waves.

Tinnitus is not itself a disease but an unwelcome symptom resulting from a range of underlying causes, including ear infections, foreign objects or wax in the ear, and injury from loud noises. Tinnitus is also a side-effect of some oral medications, and may also result from an abnormally low level of serotonin.

The sound perceived may range from a quiet background noise to a signal loud enough to drown out all outside sounds. The term 'tinnitus' usually refers to more severe cases. A 1953 study (Heller and Bergman) of 80 tinnitus-free university students placed in a soundproofed room found that 93% reported hearing a buzzing, pulsing or whistling sound. However, it must not be assumed that this condition is normal -- cohort studies have demonstrated that damage to hearing from unnatural levels of noise exposure is very widespread in industrialized countries.

Because tinnitus is often defined as a subjective phenomenon, it is difficult to measure using objective tests, such as by comparison to noise of known frequency and intensity, as in an audiometric test. The condition is often rated clinically on a simple scale from "slight" to "catastrophic" according to the practical difficulties it imposes, such as interference with sleep, quiet activities, or normal daily activities. For research purposes, the more elaborate Tinnitus Handicap Inventory is often used.