The etiology, incidence, acute and late prognosis, and treatment of sudden hearing loss (SHL) are described variously in the literature. In an 8-year prospective study of 225 SHL patients, initiated in July 1973, overall, normal, or complete recovery occurred in 45% of patients and late otologic complications in 28%. Important prognostic indicators were severity of initial hearing loss and vertigo, time to initial audiogram, and elevated erythrocyte sedimentation rate; other indicators were age greater than 60 and less than 15 years, midfrequency audiogram configuration, and hearing status of the opposite ear. A common inflammatory cause is suggested for all degrees of severity in SHL, and a prognostic table is provided to aid the practitioner in predicting recovery. There is still no evidence that treatment achieves a result better than expected with spontaneous recovery.