✓ To investigate evidence for diffuse white matter injury and hemispheric disconnection sequelae after severe closed head injury (CHI), this study evaluates the degree of posttraumatic atrophy of the corpus callosum. Corpus callosal atrophy was quantitatively determined using a digitizer to measure sagittal magnetic resonance images of 32 patients with moderate-to-severe CHI and those of 31 control subjects of similar age. In the CHI patients, measurements were significantly reduced for the areas of the anterior four-fifths, the posterior one-fifth, and the total corpus callosum. Moreover, the minimum width of the callosal body was reduced in the CHI patients as compared to that of control individuals. Indices of corpus callosal atrophy were significantly correlated with the chronicity of injury and the degree of lateral ventricular enlargement. There was no difference in callosal measurements between men and women. Magnetic resonance imaging provides an in vivo determination of corpus callosal atrophy which may reflect the severity of diffuse axonal injury and predict the type and severity of hemispheric disconnection effects.