Monocular deprivation was used to examine the experience-dependent structural plasticity of astrocytes in Oc1M and Oc1B visual cortex of young and adult rats. Stereological techniques were employed to assess the numerical density (Nv) of cells and surface density (Sv) of processes immunoreactive for glial fibrillary acidic protein in laminae II/III, IV, V and VI in the hemisphere opposite the deprived eye. In one group of pups eyelids were sutured on postnatal day 12 (P12) and maintained until P80 (MD), while a second group had the sutures removed at P75 followed by 5 days of light exposure (MD + L). An unoperated light experienced group was used for comparisons (L). The Sv of astrocytic processes in lamina IV but not laminae II/III, V and VI was significantly decreased in the MD group. The ratio of Sv to the Nv of neurons, an estimate of the amount of astrocytic membrane per neuron, was also significantly decreased in layer IV. The Nv of astrocytes was not significantly different among the three groups. In adults that were monocularly deprived for 5, 10 and 30 days the Nv of astrocytes and Sv of their processes were not significantly altered in layer IV. There was however an increase in the Nv of all types of glial cells combined in layer IV following 10 and 30 days. These results indicate that the structure of astrocytes is influenced by visual experience during development whereas merely altering the level of visually-driven activity in the adult was not sufficient to induce astrocytic structural change.