Twenty-eight patients with dementia resembling senility, and some with gait disturbance, had enlarged cerebral ventricles and were subjected to cerebrospinal fluid shunting. The cause of the ventricular enlargement was not apparent and therefore should be classified as idiopathic normal pressure hydrocephalus. A good response to shunting was achieved in 18 of 28 (64.3%) of the patients. No criteria could be established that would distinguish patients who would be expected to respond from those who would not. In particular, radioactive iodinated serum albumin (RISA) encephalography was not a reliable test for this purpose. Pneumoencephalography is indicated in all patients with organic dementia and, should enlarged ventricles be found, shunting should be done. Patients with gait disturbances as a prominent feature will respond more frequently to ventricular shunting, though not necessarily better, than patients with dementia as the most prominent feature.