Sixty-eight patients with DMD underwent psychometric assessment before or after thalamic surgery. Statistical comparisonss between categories of patients were undertaken as a function of religion, family history, and age at onset of symptoms as independent variables. It was found that Jewish patients, with negative family history, and age at onset of symptoms from 9 to 13 years, scored significantly higher on IQ tests than did all other groups. Other psychological test data revealed no specific personality patterns in the DMD patients, particularly no pattern of conversion hysteria or hysteria. Pre- and postoperative psychological testing in a small group of patients revealed no evidence of any changes in intellectual, cognitive, or personality functions as a consequence of thalamic surgery, involving up to 10 lesions in some instances.