To assess the association between the habitual head position during bedrest and the affected ear in benign paroxysmal positional vertigo (BPPV). Prospective trial of patients with active BPPV of the posterior semicircular canal, confirmed on physical examination. Seventy-five patients were asked to explain the head position and lying side they were accustomed to before falling asleep in bed. Fifty patients (67 per cent) habitually adopted a lateral head position during bedrest. The ear affected by BPPV was found to be consistent with the head-lying side during bedrest in 43 cases (86 per cent) (29 cases for the right ear and 14 cases for the left ear). Habitual lateral head-positioning during bedrest can be a major factor leading to the development of BPPV in the ipsilateral ear.