The aim of this study was to begin to parse the relative contributions of the right and left ventromedial prefrontal cortices (VMPC) in regard to social conduct, decision-making, and emotional processing. We hypothesized that the right VMPC is a critical component of the neural systems that subserve such functions, whereas the left VMPC is not. Seven participants with focal, stable unilateral lesions to the right (n = 4) or left (n = 3) VMPC were studied with procedures designed to measure social conduct, decision-making, and emotional processing and personality. The right-sided participants had profound disturbances of social and interpersonal behavior and of the ability to maintain gainful employment; they had defective performance and impaired anticipatory skin conductance responses during the Gambling Task; most had profound abnormalities of emotional processing and personality, and met criteria for "acquired sociopathy." By contrast, the left-sided participants had normal social and interpersonal behavior; they had stable employment; they performed normally and had normal skin conductance responses on the Gambling Task; they had normal emotional processing; and their personalities were unchanged from premorbid status. The marked deficits in social conduct, decision-making, and emotional processing in participants with unilateral right VMPC lesions are reminiscent in kind of those that have been reported in connection with bilateral VMPC lesions, albeit perhaps of lesser severity. The findings provide preliminary evidence that insofar as social, decision-making, and emotional functions are concerned, the right-sided component of the VMPC system may be critical, whereas the left-sided component may be less important.