Isolated cortical venous thrombosis (CVT) is rare, and the discrepancy between clinical features and neuroradiologic findings has not been adequately emphasized. A thirty-one-year-old woman presented with focal seizures and occasionally secondary generalization. There was no focal neurologic deficit except for Todd's paralysis. Electroencephalography showed intermittent theta waves at the left frontoparietal area. Brain computed tomography (CT) and magnetic resonance imaging (MRI) disclosed a large lesion in the left frontoparietal area. An extensive occlusion of the superior cerebral veins of the left hemisphere with a patency of the dural sinuses was noted in the cerebral angiography. Eight months later, the CT hypodense lesion disappeared. Her neurologic status was stationary, but the seizures, mostly focal, still occurred occasionally. In this report, the authors emphasize the dissociation between minor clinical features and larger CT and MRI lesions in isolated CVT.