In a series of 100 patients with unilateral acoustic neuroma the incidence of mastoid aching was found to be 25 per cent, though none of the patients reported this as their principal symptom. Mastoid ache was not related to tumour size, hydrocephalus, or duration of symptoms. However, there was a significantly higher incidence of facial numbness and diminished facial sensation, but not facial weakness, compared with the whole series. Since motor fibres are more resistant to pressure than sensory fibres, mastoid ache may signify the pressure of an expanding cerebellopontine angle tumour.