Baylisascaris procyonis, the ascarid of raccoons, causes a characteristic, rapidly fatal eosinophilic meningoencephalitis with ocular involvement in many naturally and experimentally infected aberrant hosts, including monkeys. Warnings that humans are potentially susceptible to the devastating infection have been issued, but an instance in humans has not been recognized. This report describes a boy who died from an eosinophilic meningoencephalitis, which mimicked B. procyonis infection in monkeys. The causative agent was not identified during life. Autopsy showed a systemic larval ascarid infection with massive involvement of the brain. The size and anatomy of the larvae in histologic sections were identical to those recorded for B. procyonis. The larvae were indistinguishable from the B. procyonis larvae observed in histologic sections of experimentally infected monkeys. An indirect immunofluorescence test was positive for B. procyonis. Exposure to raccoon feces was highly likely. The evidence suggests that this is the first recognized B. procyonis infection in humans. Prudent avoidance of exposure to raccoon feces is indicated.