Autism is a neurodevelopmental disorder characterized by deficits in language and communication. Previous research examining gray and white matter structure in children with autism has revealed abnormalities in regions critical for language. Studies that have related anatomical brain development to language performance often rely on standardized tests of language. These studies provide a limited portrait of language ability and do not examine language in real world contexts such as in a spoken narrative. In a recent study of narrative performance, 17 typically developing (TD) children and 11 children with high functioning autism (HFA) six to 13 years of age told a story of an instance when they had a conflict with another person. In their narratives, children with HFA had deficits in morphology and syntax. In order to understand the brain basis of spontaneous language in TD children and children with HFA, the current study investigated the relationship between magnetic resonance imaging (MRI)-based measures of gray and white matter structure and morphosyntactic performance during their spoken narrative. In the TD group, there were systematic associations between gray matter development and children's use of morphology and syntax. Gray matter structure was related to narrative performance in left inferior frontal gyrus (Broca's area), the right middle frontal sulcus, and the right inferior temporal sulcus. Associations between gray matter structure and narrative performance were not found in children with HFA. These findings suggest a systematic coupling between brain structure and spontaneous language in TD children and a disruption of these relationships in children with HFA. In the analysis of white matter development, fractional anisotropy (FA), a measure of white matter coherence and organization, was assessed in major cerebral white matter tracts. In the TD group, FA correlated with morphosyntactic production in the traditional language pathway, the left arcuate fasciculus. In contrast, associations between morphosyntax and white matter in the HFA group were found with the inferior longitudinal fasciculus, a ventral pathway thought to mediate visual and perceptual stimuli, and with corticostriatal fibers responsible for motor planning and articulation. Such evidence suggests that white matter development in pathways responsible for visual processing and articulation are important for mediating spoken language in children with HFA. Conversely, it appears that TD children may rely on pathways connecting traditional language regions such as a Broca's and Wernicke's area. The current study is the first to demonstrate links between gray and white matter development and spontaneous real world language production.