ObjectiveTo demonstrate a causal relationship between bone dust and the development of headache after retrosigmoid removal of acoustic neuromas.Study DesignThe study design was both retrospective (group 1) and prospective (groups 2 and 3).SettingTertiary Care Referral Center/Outpatient Data Collection.PatientsEighty-four consecutive patients underwent surgery at the Mount Sinai Medical Center in New York by the same surgical team.InterventionAll patients underwent retrosigmoid removal of acoustic neuromas via the following methods: group 1, standard excision; group 2, excision and cranioplasty; group 3, excision, cranioplasty, and residue trapping.Main Outcome MeasurePresence or absence of postoperative headache.ResultsIn all, 43 patients (51%) reported postoperative headache. By groups, headache incidence was 64% for group 1 (43% grade 3–4), 81% for group 2 (37% grade 3–4), and 10% (all grade 1) for group 3. Differences with respect to headache incidence and severity were statistically significant between groups 1 and 3, and between groups 2 and 3 (p < 0.001).ConclusionsFree circulation of bone dust into the posterior fossa during intradural drilling of the internal auditory canal may be the most important factor in the development of headache after this surgical procedure.