Disorders of peroxisome function result in severe and progressive neurologic deficits. Knowledge of these disorders and their role in neurodegenerative disorders has been growing rapidly over the last 40 years. Noninvasive diagnostic tests can identify all of the peroxisomal disorders, many of them prenatally. The genetic basis of some of these peroxisomal disorders is being established, which will advance understanding of their pathobiology and provide clues for therapeutic interventions.