Autism is a developmental disorder with variable severity, occurring at all levels of cognitive ability and having a number of slightly different clinical presentations. It is associated with neuropsychological deficits that occur in other conditions also, but its pattern may be specific to autism. Genetic and environmental early insults to brain development are etiological determinants of the disorder. Brain circuitries important for social, communicative, and integrational purposes have been suggested to be dysfunctional in autism. There could be at least two different pathways to autism, one connected with primary temporofrontal dysfunction (and late prenatal–early postnatal origins) and another linked to primary brain-stem dysfunction (and early prenatal origins). Further study of neurodevelopmental and neuropsychological processes in autism will help elucidate not only the pathological mechanisms involved in the specific syndromes but also the underpinnings of normal brain development.