Asymmetrical sensorineural hearing loss is usually investigated thoroughly but a diagnosis is often elusive. It is important to identify any treatable causes. Lyme disease is a tick-borne infection caused by the spirochaete Borrelia burgdorferi, which has been shown to cause asymmetrical sensorineural hearing loss, and has been successfully treated. Its incidence varies regionally; it occurs where there is a suitable environment for the tick and its animal hosts. We conducted a prospective study of 100 patients with asymmetrical sensorineural hearing loss. Serological testing for Lyme disease was performed. One patient had positive serology, but there was no improvement in her hearing following antibiotic treatment. We cannot conclude that our patient's hearing loss was caused by Lyme disease. We suggest that routine screening is not cost effective in regions with a low incidence of Lyme disease.