Sudden deafness sometimes has an identifiable cause, but in most cases the cause is unknown (idiopathic sudden deafness). Vascular impairment has been proposed as an aetiological mechanism for this condition, but it is unclear whether traditional cardiovascular risk factors, such as smoking or alcohol intake, are associated with this condition. We accordingly investigated associations of idiopathic sudden deafness with smoking, alcohol intake and sleep duration in a case-control study. Cases were consecutive patients diagnosed with idiopathic sudden deafness between October 1996 and August 1998 at collaborating hospitals in Japan. Controls were obtained from a nationwide database of pooled controls, with matching for age, gender and residential district. Exposure variables were assessed from a self-administered questionnaire. Subgroup analyses were performed using audiometric subtypes of sudden deafness. Data were obtained for 164 cases and 20,313 controls. Increased risks of idiopathic sudden deafness were observed among participants who consumed two or more units of alcohol per day (OR=1.90, 95% Cl=1.12-3.21), and among participants who slept less than seven hours per night (OR=1.61, 95% Cl=1.09-2.37). The direct association with alcohol intake was particularly strong for the participants with profound hearing loss. There was little evidence of an association with smoking. This study suggests that alcohol intake and short sleep duration might be risk factors for idiopathic sudden deafness. sudden deafness, case-control study, smoking, alcohol, sleep.