We describe the clinical and laboratory features of 13 patients with bilateral loss of peripheral vestibular sensitivity of no known cause. In the office, screening for this condition was possible using illegible e- testing and examination of the patient for refixation saccades after brisk head movements while attempting visual fixation. Diagnosis was confirmed by bilaterally reduced caloric responses (<20 degrees/second on all 4 caloric irrigations) and abnormally low gain of the vestibuloocular reflex on rotational chair testing. The mean age of the patients was 68 years. We noted two patterns of symptom onset: onset associated with vertigo (10 patients) and Insidious progressive disequilibrium not associated with vertigo (3 patients). Only 38% of the patients complained of subjective oscillopsia. The subjects performed poorly on platform posturography, particularly when deprived of visual and somatosensory feedback. When associated with vertigo, bilateral vestibular loss may be the result of bilateral sequential vestibular neuritis; when not associated with vertigo, disequilibrium may be caused by slow, symmetrical loss of peripheral function as a result of aging. Although the subjects in this report were elderly, idiopathic bilateral vestibular loss has been reported in patients of all ages.