An outbreak of cerebrospinal nematodiasis due to Baylisascaris sp. was documented in an urban outdoor aviary in southern California. Thirty-four out of 35 cockatiels ( Nymphicus hollandicus, 97%) showed a variety of neurological signs including ataxia, lateral recumbency, opisthotonus, and torticollis. Thirteen carcasses were submitted for necropsy; the histological lesions were restricted to the central nervous system (brain and spinal cord) and were predominantly degenerative, characterized by multifocal white matter vacuolation, gliosis, axonal swelling, gitter cell infiltration, and mild hemorrhage, rarely accompanied by mild granulomatous inflammation and mild lymphocytic perivascular cuffs. Nematode larvae morphologically compatible with Baylisascaris sp. were observed in the brain of 5 birds, away from the lesion site.