Tinnitus is a variety of sound that is heard when no corresponding external sound is present. Nearly everyone experiences faint "normal tinnitus" in a completely quiet room; but it is of concern only if it is bothersome, interferes with normal hearing, or is associated with other problems. The word tinnitus comes from the Latin tinnire, "to ring". In some people, it interferes with concentration, and can be associated with anxiety and depression.

Tinnitus is usually associated with hearing loss and decreased comprehension of speech in noisy environments. It is common, affecting about 10–15% of people. Most tolerate it well, and it is a significant problem in only 1–2% of people. It can trigger a fight-or-flight response, as the brain may perceive it as dangerous and important.

Rather than a disease, tinnitus is a symptom that may result from a variety of underlying causes and may be generated at any level of the auditory system as well as outside that system. The most common causes are hearing damage, noise-induced hearing loss, or age-related hearing loss, known as presbycusis. Other causes include ear infections, disease of the heart or blood vessels, Ménière's disease, brain tumors, acoustic neuromas (tumors on the auditory nerves of the ear), migraines, temporomandibular joint disorders, exposure to certain medications, a previous head injury, and earwax. It can suddenly emerge during a period of emotional stress. It is more common in those with depression.

The diagnosis of tinnitus is usually based on a patient's description of the symptoms they are experiencing. Such a diagnosis is commonly supported by an audiogram, and an otolaryngological and neurological examination. How much tinnitus interferes with a person's life may be quantified with questionnaires. If certain problems are found, medical imaging, such as magnetic resonance imaging (MRI), may be performed. Other tests are suitable when tinnitus occurs with the same rhythm as the heartbeat. Rarely, the sound may be heard by someone other than the patient by using a stethoscope, in which case it is known as "objective tinnitus." Occasionally, spontaneous otoacoustic emissions, sounds produced normally by the inner ear, may result in tinnitus.

Measures to prevent tinnitus include avoiding chronic or extended exposure to loud noise, and limiting exposure to ototoxic drugs and substances. If there is an underlying cause, treating that cause may lead to improvements. Otherwise, typically, tinnitus management involves psychoeducation or counseling, such as talk therapy. Sound generators or hearing aids may help. No medication directly targets tinnitus.