The authors review 17 cases of aqueductal stenosis in adults and describe five modes of clinical presentation. The average duration of symptoms was 6 years. Dementia was infrequent. Skull x-ray films frequently demonstrated some degree of cranial enlargement and signs of chronic increased intracranial pressure. Characteristic alterations of the sella included elongation of the anterior wall and flattening, erosion, and anterior displacement of the dorsum. Aqueductal configurations as defined by ventriculography and pneumoencephalography in all cases, and the angiographic findings in seven cases are described. Most of the patients improved substantially after shunt insertion. The clinical findings suggested that aqueductal narrowing and associated hydrocephalus had been present in most of these patients since early life.