Twenty-four psychological test scores including measures of psychometric intelligence, abstraction ability and measures of motor and sensory performance were obtained for each of 97 neurological patients with planographic and linear measurements of the area of the cella media and linear measurements of the Illrd ventricle as seen in anteriorposterior projection of PEGs. While statistically significant differences were found in only one third of each of these three intergroup comparisons, lower mean performance was associated with the largest combined measurement ventricle group that with the smallest combined measurement ventricle group in 21 of 24 tests when groups were composed according to planimeter measures; in 20 of 24 tests in linear measurement groups, and in 24 of 24 comparisons between largest and smallest Illrd ventricle groups. Discrepancy scores based upon differences in performance on the right and left body side were computed for four groups composed according to largest and smallest R/L ventricle ratios, using planimeter and linear measurements. Discrepancy scores consistent with the side of greater asymmetry were found in 17 of 20 motor and sensory tests when groups were composed according to planimeter measures, but in only 13 of 20 tests when linear measurements were used to compute the ratios. Largest right versus smallest right and largest left versus smallest left ventricle groups were composed without regard for size of the other lateral ventricle or Illrd ventricle measurement in each subject, and intergroup comparisons were made of motor and sensory test performance on the contralateral body side. Poorer contralateral performance was found in 18 of 20 measures in the large right ventricle group and in 17 of 20 measures in the large left ventricle group, with approximately one-third of the measures yielding significant differences in each comparison. In general, the results suggested that less adequate psychometric intelligence, abstraction ability and bilateral performance on motor and sensory tests was associated with large as opposed to small lateral ventricle and Illrd ventricle groups. Lateralized motor and sensory deficits consistent with lateral ventricle size or asymmetry ratios were also demonstrated, with better intergroup separation achieved using planimeter than linear measurements. Verbal and Performance IQ scores and results on a test of abstraction ability did not show significant differences as a function of side of ventricle enlargement.