In order to investigate risk factors for idiopathic sudden sensorineural hearing loss (sudden deafness), a case-control study was done in 109 patients with sudden deafness who visited our hospital between 1992 and 1994, with 109 controls matched to each patient by gender and age. Odds ratio (OR) and 95% confidence interval (CI) for smoking habits, drinking habits, dietary habits, environmental noise, past history of disease, sleeping hours, appetite, fatigue, incidence of common cold were obtained. Fatigue (OR: 3.28; 95% CI: 1.36-7.90) and loss of appetite (OR: 8:00; 95% CI: 1.00-64.0) elevated the risk for sudden deafness. Those who ate many fresh vegetables were at a decreased risk (OR: 0.48; 95% CI: 0.24-0.96 for light-colored vegetables, OR: 0.55; 95% CI: 0.30-1.02 for green-yellow vegetables). Personal histories of hypertension and thyroid disease, and susceptibility to colds appeared to be positively associated with the risk (0.05 < P < 0.10). Smoking habits, drinking habits and environmental noise had no significant association with sudden deafness. These results suggested that environmental factors, including diet, may be importantly involved in the genesis of sudden deafness.