We present a consecutive series of 8 patients who developed a manic episode after a brain injury. Five patients had cortical lesions (4 with damage to the right basotemporal region, and 1 with bilateral damage to the orbitofrontal area). while the other 3 patients had subcortical lesions (white matter of the right frontal lobe, right anterior limb of the internal capsule, and right head of the caudate), a 18fluorodeoxyglucose positron emission tomography scan showed hypometabolism in the right lateral basotemporal region in all 3 patients. These findings suggest a major role for the basal region of the right temporal lobe in the modulation of mood.