Baylisascaris procyonis is a common and widespread parasite of raccoons in the United States and Canada. With large raccoon populations occurring in many areas, the potential risk of human infection with B procyonis is high. We report a case of severe raccoon roundworm (B procyonis) encephalitis in a young child to illustrate the unique clinical, diagnostic, and treatment aspects, as well as public health concerns of B procyonis infection. Acute and convalescent serum and cerebrospinal fluid samples from the patient were tested for antibodies against B procyonis to assist in documenting infection. An extensive field survey of the patient's residence and the surrounding community was performed to investigate raccoon abundance and to determine the extent of raccoon fecal contamination and B procyonis eggs in the environment. The patient evidenced serologic conversion, and the field investigation demonstrated a raccoon population far in excess of anything previously reported. There was abundant evidence of B procyonis eggs associated with numerous sites of raccoon defecation around the patient's residence and elsewhere in the community. Because B procyonis can produce such severe central nervous system disease in young children, it is important that pediatricians are familiar with this infection. The public should be made aware of the hazards associated with raccoons and B procyonis to hopefully prevent future cases of B procyonis infection.