[3] Read before the Sioux Valley Medical Association, July 22, 1914, and published in these columns at the request of the Association. The most important causes of intracranial complication from the middle ear and nasal accessory sinuses, are suppurations, consequently I shall confine my remarks to that subject, and not take up the neoplasms, trauma, etc. In the diagnosis it is most important to recognize suppurative disease of the ear and sinuses, but this subject is not within the province of this paper, therefore I shall satisfy myself by mentioning only that the presence of the pus from the middle ear and nose, and Röntgenographic examination, are the most important signs of affections of these structures. The one symptom more than any other on the part of the patient of a threatening extension into the cranial cavity, is localized pain or headache, which is very persistent, instead of periodic. Especially important is this in connection with the cessation or diminution of the discharge. The knowledge of the pathological change present in the sinuses and middle ear and mastoid, is of additional value as, for instance, tuberculosis, syphilis, and cholesteatoma. The frequency of intracranial complication in suppuration of the middle ear is much greater than that following sinus disease, about twenty-five to one in my experience. The intracranial complications which I shall consider are-- 1. Meningitis. 2. Sinus thrombosis. 3. Brain abscess. The meningitis may be serous or suppurative, and later localized or diffuse. The sinus thrombosis may be partial or parietal, and complete with or without involvement of the jugular bulb and vein. The brain abscess may be extradural or genuine within the brain substance proper. The complications may be further divided as to bacteriologic or etiologic factors as, for instance-- Streptococcic Staphylococcic Pneumococcic Tuberculous Syphilitic These complications may arise following acute, or chronic and acute, exacerbation of chronic suppuration of the ear and sinuses. Meningitis and sinus thrombosis (this latter condition is very frequently associated with a localized meningitis) are usually complications following acute, or acute exacerbation of chronic, suppuration of the ear and sinuses. Brain abscess, however, is most frequently associated with the chronic form of the ear and sinus disease; but these become more manifest following an acute attack of ear or sinus trouble. Tubercular or syphilitic meningitis is chronic inflammation _per se_; but these conditions are also lit up by the acute processes within the ear and sinuses. The cardinal symptoms of any intracranial complications are-- 1. _Pain or headache._--This may be localized or diffuse; it is, however, very persistent and quite intense. It is in the recognition of this symptom that has helped me more than any other in suspecting intracranial trouble.