A remarkable case of spontaneous meningeal fistula of the middle ear is described, the lesion being detected during insertion of a trans-tympanic aerator in an 80-year-old woman. The totally exceptional nature of this case is emphasized, and the therapeutic problems that it gave rise to exposed. Instead of the suprapetrous approach, theoretically more logical, the less dangerous inferior approach was employed, with a subsequent successful result. Biochemical tests should be conducted in all cases of serous otitis, where there is secretion of an abundant amount of clear fluid of atypical appearance.