While neuroimaging studies have reported neurobiological abnormalities in autism, the underlying tissue abnormalities remain unclear. Quantitative transverse relaxation time (T2) imaging permits the examination of tissue abnormalities in vivo, with increased T2 largely reflecting increased tissue water. Blood flow and the presence of tissue iron may also affect T2. In this study, we used voxel-based relaxometry of the cerebrum and global averages to examine T2 abnormalities in autism. Nineteen males with autism (age: 9.2 +/- 3.0 years) and 20 male controls (age: 10.7 +/- 2.9 years) underwent magnetic resonance imaging at 3.0 T. Quantitative T2 maps, generated through gradient echo sampling of the free induction decay and echo, were segmented into gray matter, white matter, and cerebrospinal fluid. Average cerebral gray and white matter T2 were determined and compared between groups. To assess localized T2 differences, the quantitative T2 maps were warped to a template created for this study, smoothed, and compared using statistical parametric mapping. Patients with autism had an increase in average cerebral white matter T2, although no group differences were seen in average cerebral gray matter T2. Patients with autism also had bilateral regional T2 increases in the gray matter and associated white matter of the parietal lobes (primary sensory association areas) and occipital lobes (visual association areas) and in the white matter within the supplementary motor areas in the frontal lobes. The regional and global elevations in white matter T2 suggest abnormalities of white matter tissue water content in autism, which may represent a neurobiological basis for the aberrant cortical connectivity hypothesized to underlie the disorder.