After bilateral ablation of orbital and lower mesial frontal cortices, a patient had profound changes of behavior that have remained stable for 8 years. Although he could not meet personal and professional responsibilities, his "measurable" intelligence was superior, and he was therefore considered a "malingerer." Neurologic and neuropsychological examinations were otherwise intact. CT, MRI, and SPET revealed a localized lesion of the orbital and lower mesial frontal cortices. All other cerebral areas had normal structure and radioactivity patterns. Such impairments of motivation and complex social behavior were not seen in control cases with superior mesial or dorsolateral frontal lesions.