THE IDEA that the structures of the frontal lobe play a critical role in normal social behavior is now well established. The association was first gleaned more than a century ago thanks to the case of Phineas Gage, in whom focal damage to unspecified frontal regions (Gage died without an autopsy and only his skull was recovered) resulted in a sudden and profound change of personality marked by inappropriate social behavior. More recently, it has become clear that several sectors of the prefrontal cortex contribute to the acquisition and manipulation of the type of knowledge on which adaptive social behaviors depend. Some prefrontal sectors (in particular, those that are located in the orbital and medial surfaces of the frontal lobes) seem to play an indispensable role in the achievement and maintenance of a normal social personality. Lesions that compromise these frontal sectors or their subjacent white matter that are located either bilaterally or only in the right hemisphere impair the ability to make appropriate decisions in the personal and social realms.^1-4