Recent reports have suggested that particulate matter identified within the membranous portion of the posterior semicircular canal is responsible for the development of positional vertigo. To further investigate this claim, a posterior canal fenestration was carried out in ten patients undergoing acoustic tumor removal via a translabyrinthine approach. Particles were identified in the membranous labyrinth in nine patients. One of these patients described positional vertigo preoperatively. Electron microscopy demonstrated particles within the membranous labyrinth that appeared to be of mixed proteinaceous and mineral content. These data suggest that further studies must be undertaken before the theory of endolymphatic particle migration can be confirmed as the etiology of positional vertigo.