The telencephalic hemispheres and the optic tectum of the turbot Scophthalmus maximus were analysed volumetrically during metamorphosis. Both brain regions develop an asymmetry coordinated chronologically with metamorphic events that produce asymmetry in the rest of the animal. Furthermore, the brain asymmetries are correlated with, and may be determined by, the side of origin of their primary afferent inputs, such that the more voluminous side of the brain receives these inputs from the zenithal side. After metamorphosis, the telencephalon remains asymmetric, whereas the optic tectum recovers its bilateral symmetry.