Transcranial color-coded duplex sonography is a recently introduced method for visualizing (1) the blood flow velocity of the basal cerebral arteries and (2) the brain parenchyma as an acoustic impedance image. Dislocation of the third ventricle due to space-occupying stroke is an important clinical marker. This study evaluated the dislocation of the third ventricle from the brain midline by transcranial duplex sonography in 10 healthy volunteers. The mean dislocation was 0.2 +/- 0.3 mm. Eighteen stroke patients were investigated within 12 hours by both duplex sonography and computed tomography (CT) and the dislocation of the third ventricle was measured. Correlation between the two methods was high (r = 0.87, N = 27). Twelve stroke patients divided into three subgroups according to the extent of the space-occupying effects of the lesion were followed for 3 weeks. The increase and decrease of the dislocation of the third ventricle over the time were monitored. In conclusion, transcranial duplex sonography is a reliable tool to monitor dislocation of the third ventricle due to space-occupying stroke.