This study aimed to characterize cerebral perfusion in men with Klinefelter's syndrome, known to present specific deficits in language, using (99m)Tc- hexamethylpropylene-amine-oxime scintigraphy and Talairach normalization. While a perfusion asymmetry toward the left hemisphere was found in controls, perfusion was mostly symmetrical in Klinefelter patients in the upper temporal and lower parietal areas. Scores on verbal tests were inversely correlated with perfusion changes, providing neurobiological substrate of anomalous cerebral laterality.