Epidermoids are rare tumors which occur either extradurally in the diploë of the skull or as intradural lesions involving various portions of the brain and occasionally the spinal cord. According to Bennett (3), the incidence of epidermoids of the central nervous system at the Army Institute of Pathology was 5 cases in 518 brain tumors or 0.96 per cent. He quotes other statistics which indicate a variation in incidence from 0.37 to 0.6 per cent. These lesions are often referred to as cholesteatomas and pearly tumors because they usually contain large amounts of cholesterol and, when encountered at operation, grossly present a mother-of-pearl sheen. The term epidermoid is preferred because it is believed that the tumor arises from embryonic epithelial rests (7) and is not merely the result of epithelial debris such as is found in the middle ear and mastoid region. There have appeared in the literature many reports (1–5, 7, 10, 11, 13, 14, 16,) indicating that diagnosis of the intracranial lesions is seldom made preoperatively and that many of them are incidental findings postmortem. The extradural or diploic epidermoids are often diagnosed before operation by the radiographic demonstration of a scalloped, sharply circumscribed destructive area in the skull (13). The intraventricular epidermoids produce a characteristic pneumoencephalographic appearance, of which only 6 verified cases have been found in the literature. Krieg (12), in 1936, in a report of aseptic meningitis following operation in two cases of cholesteatoma, described in the ventriculograms of one case irregular circular dense shadows in the air-filled right lateral ventricle. In a footnote he stated that similar findings had been previously demonstrated by Olivecrona in ventriculograms which were typical for cholesteatoma. Dyke and Davidoff (9), in 1937, without the knowledge of Krieg's publication, reported a large epidermoid tumor located in the temporal and frontal horns of the right lateral ventricle with surgical removal and uneventful recovery. The air studies described were unique, showing globular and linear collections of gas in the area normally occupied by the thalamus, the island of Reil, and the right temporal and posterior portion of the frontal lobes. In addition, the left lateral ventricle was larger than the right, the body of the latter being elevated. The third ventricle was displaced to the left, and the right temporal horn was sharply cut off. Weinberger (17), in 1938, made the diagnosis of an intraventricular epidermoid from the encephalographic appearance in an unproved case, and also reported a second case with characteristic air studies which had been operated on by Dr. Sydney W. Gross. The latter patient made an uneventful recovery, with only a residual slight speech defect.