Projections from visual thalamus to posterior cortex of the Virginia opossum revealed by retrograde transport of horseradish peroxidase show a specific and orderly pattern. The lateral geniculate nucleus projects only to cortical area 17, while a lateral sector of the lateral posterior nucleus sends afferents both to areas 17 and 18. Area 19 receives input from the lateral intermediate nucleus; the caudomedial sector of the lateral posterior nucleus projects to the anterior and posterolateral areas of cortex. These features are generalized to other mammals to include thalamic input differentially derived from retinal, tectal, pretectal and cortical sources.