Magnetic resonance (MR) imaging scans of 33 traumatically brain-injured (TBI) patients were compared quantitatively to MR scans of controls matched for age and gender. Quantitative estimates of thalamic, internal capsule, and third ventricle morphology were obtained in each TBI patient. Comparisons were made to normal control subjects and revealed significant reduction in thalamic volume with corresponding increase in third ventricle. Measurements of internal capsule reflected nonsignificant changes. Significant correlations were observed between sensory-perceptual functioning, as measured by the Reitan-Kløve Sensory-Perceptual Exam, and thalamic volume in TBI patients. A decrease in thalamic volume was associated with an increase in sensory-perceptual errors.