Avian cerebrospinal nematodiasis was studied in chickens experimentally inoculated with infective eggs of Baylisascaris procyonis of raccoon origin. Birds each received 3,200, 1,600, 800, 400, 200, or 0 eggs, one dose per group of 10 birds. Central nervous system (CNS) disease developed in 17 of the 50 infected birds. Birds receiving the higher dosages exhibited the worst clinical signs, had higher mortality rates, lived for shorter duration, and had the most severe brain lesions. Onset of CNS disease was consistent between groups and averaged 20.4 days, and duration varied from less than one to 23 days. No gross lesions were present. Histologically, multifocal areas of malacia and necrosis, hemorrhage, perivascular cuffing, nonsuppurative meningoencephalitis, focal granulomas, and migrating larvae were seen in the brains. No larvae were recovered from the brains by the Baermann method. Extraneural lesions were limited to focal choroiditis and a granuloma in an extrinsic ocular muscle.