Differentiating balance disorder patients who are malingering from those with organic balance disorders is difficult and costly. We used trunk sway measured during several stance and gait tasks in 18 patients suspected of malingering in order to differentiate these from 20 patients who had suffered unilateral vestibular loss 3 months earlier, 20 patients with documented whiplash injuries, and 34 healthy controls. Classification results ranged from 72 to 96% and were equally accurate for task or criteria variables based on 90% sway values. The tasks yielding the best discrimination were: standing with eyes closed on a foam and firm surface; standing with eyes open on a firm surface; standing on 1 leg; and walking tandem steps. The criteria yielding the best discrimination were: standing with eyes open on a firm surface; the difference between standing with eyes closed on foam and firm surfaces; the difference between walking tandem steps and standing on 1 leg with eyes open; and the difference between roll and pitch velocity when walking 8 tandem steps. We conclude that discriminating suspected malingering balance disorder patients is possible using variables or criteria based on objective measures of trunk sway during several stance and gait tasks.