A survey of 67 patients with 74 mastoid cavities has been carried out. During the study period they made a total of 126 cavity/outpatient visits. Thirty-five patients (56 per cent) had discharge from at least one cavity on at least one outpatient visit. At only 5 per cent of visits was the discharge classified as profuse. A retrospective study of 54 mastoid revision operations on 51 patients has been made. Overall 59 per cent of operations resulted in a dry ear. The best results were achieved by carrying out cavity revision combined with a meatoplasty (83 per cent dry ears). Cavity revision alone produced a dry ear in only 57 per cent of cases. The worst results were produced by soft tissue obliteration (33 per cent dry ears). This supplement also presents the early results of a prospective investigation of bone pate obliteration of mastoid cavities. Of the eight cases studied so far, five (63 per cent) have dry ears following surgery. Three of the patients in this group had undergone previous unsuccessful revision surgery using other techniques. Cavity revision with meatoplasty is the technique of choice for most patients, but mastoid obliteration offers potential advantages for younger patients, particularly those wishing to swim.