The present study was designed to assess the architectural organization and extent of the entire mouse visual cortex. We used nonphosphorylated neurofilament protein, a selective neuronal marker that exhibits region-specific cellular and laminar distribution patterns, to delineate cortical subdivisions. A comprehensive documentation of immunocytochemical patterns demonstrated that the pyramidal and non-pyramidal neurons expressing neurofilament proteins display striking laminar and regional patterns in the mouse visual cortex. These characteristic distribution profiles of neurofilament protein immunoreactivity permitted the delineation of the primary visual cortex (V1) and of seven extrastriate cortical areas with unequivocal anatomical boundaries. Interestingly, we distinguished four subdivisions rostromedially to V1 providing clear evidence that the cortex medial to the primary visual field is not a homogeneous region in the mouse brain. We investigated in parallel the responsiveness of these eight areas to visual manipulations based on the expression profiles of two Immediate early genes, c-fos and zif-268, both markers of neuronal activity, to ascertain the visual nature of all subdivisions caudal, rostromedial, and lateral to V1, and to localize individual neurons that became activated or deprived following different paradigms of visual experience. The present data indicate that neurochemical subdivisions of the mouse visual cortex exist not only laterally but also rostromedially to V1, and reveal highly specific organizational and functional characteristics at the cellular and regional levels.