Normal pressure hydrocephalus (NPH) is a relatively new neurologic disorder first described by Salamon Hakim of Bogotá, Colombia, in 1965. NPH is characterized by three symptoms - impaired gait, incontinence and dementia - and an anatomic abnormality, i.e., enlargement of the cerebral ventricles, which can be seen on computerized tomographic or magnetic resonance imaging. Surprisingly, the intracranial pressure is normal. The first author of this article, a Yale Medical School faculty member, developed NPH over the decade from 1992 to 2002, during which it was erroneously diagnosed as cerebral atrophy and/or Parkinson's disease. On recognizing the lack of awareness of NPH by physicians, he initiated a survey to explore this problem. He interviewed 166 practicing physicians who graduated from 50 American and 33 foreign medical schools, using a one-page, 10-point questionnaire (Part I). Almost one-third of the physicians had never heard of NPH. One-fifth had learned of NPH in medical school, and about half learned of it after medical school. Because there were insufficient physicians surveyed from 1986 to 2005, we recruited 118 additional physicians from the 20 Yale Medical School graduating classes from 1986 through 2005 (Part II). Two-thirds of them had learned of NPH in medical school, and one-fourth during residency and fellowship. Seven percent had never heard of NPH. The significance of these studies is discussed.