OBJECTIVE To assess the diagnostic usefulness of posturography in 2 well-defined patient groups with impaired balance. METHODS Ten control subjects, 10 patients with bilateral vestibular loss, and 10 patients with cerebellar atrophy. METHODS Amplitude, velocity, and frequency of sway in the anteroposterior and medial-lateral directions on a static platform, on foam, and on a moving platform. RESULTS Both patient groups consistently had increased sway compared with controls, particularly when standing on foam or on a moving platform with eyes closed. Sway amplitude and velocity were increased about the same amount. The Romberg ratio (sway with eyes closed/sway with eyes open) did not reliably differentiate patients from controls or the 2 patient groups from each other. Some patients with cerebellar atrophy exhibited a characteristic body tremor at about 3 Hz in the anteroposterior direction. CONCLUSIONS Although sway amplitude and velocity were consistently increased in patients with bilateral vestibular loss and patients with cerebellar atrophy, none of the posturography measurements reliably distinguished the 2 patient groups. The finding of increased frequency of sway in the anteroposterior direction in patients with cerebellar atrophy was of limited value since the tremor was visible at the bedside.