This paper deals with the confusion of a certain anomalous condition of the human skull with one type of trepanation. Evidence is presented to show that many specimens exhibited as examples of a certain type of trepanning are clear-cut cases of this congenital bilateral fenestra in the parietal bones. As is generally known, trephining was performed by ancient man to relieve certain maladies such as headaches caused by “demons kicking up a fuss” inside the skull. The excruciatingly painful operation was performed with a crude knife, piece of glass, or sharp-edged stone. Trephining probably flourished in Neolithic times, especially in Bohemia and western Europe. Trephined skulls have been, reported from Bolivia,, Central America, Mexico, Peru, and various other localities.