C YSTICERCOSIS of the brain and its envelopes manifests itself clinically as a kaleidoscopic disease with such a variety of symptoms and signs comparable only to the clinical manifestations of multiple sclerosis. This extreme variability is understandable when one becomes familiar with the biology and pathology of this parasitic disorder of the nervous system. In ~767 cases of unselected autopsy material reviewed from January 1954 up to December 1959 at the Unit of Pathology, Hospital General of Mexico City, U.N.A.M., 97 cases of cysticercosis were found. This is an incidence of 3.5 per cent in the material reviewed. Macroscopic Findings. The type of lesions encountered in cerebral cysticercosis depends on several factors : the time elapsed following the infection; the number of parasites that reach the nervous system and the possibility of immune allergic reaction. Escobar and Nieto described four essential forms: a) meningeal, b) ventricular, c) pareuchymatous, and d) mixed forms. The meningeal and ventricular forms are predominant, a fact in accordance with our own studies and those of others (Guccione, Sato, Stepiefi, Chordbski, Henneberg, and others). LSpez Albo, in his excellent monograph, stated that since the blood stream is the path through which the nervous system is invaded, and the oncospheres are conveyed by the circulation of the ccrebrospinal fluid, it is easy to explain the frequency of this location. Though the vesicles lodge in any part of the anterior, middle or posterior fossa, inside or outside the brain, they also can be present in the spinal canal, but this rarely happens. In a brain with recent invasion, the parasites are small and solid but soon develop into the vesicular form. If a FIG. l. Typical arachnoidal adhesions of the base in a brain invaded by Cysticerci.