A 69-year-old man presented with mild left-sided hemiparesis of 2 years' duration. A computerized tomography scan revealed a left-sided chronic subdural hematoma and a midline shift to the right. Magnetic resonance (MR) imaging obtained on admission to the hospital also disclosed a deformity of the right crus cerebri. After drainage and irrigation of the hematoma through a single burr hole, the left hemiparesis improved significantly. Magnetic resonance imaging performed 9 days after the operation revealed that the size of the subdural hematoma had diminished and the deformity of the crus cerebri had improved markedly. Kernohan's notch, caused by a supratentorial mass and producing ipsilateral hemiparesis or hemiplegia, is rarely demonstrated radiographically. This may be the first reported case in which Kernohan's notch in chronic subdural hematoma has been demonstrated on MR imaging.