Direct projections from the reuniens nucleus to the cerebral cortex were examined using the anterograde tracing method of Phaseolus vulgaris leucoagglutinin (PHA-L) in the rat. The reuniens nucleus was found to project to widespread cortical regions. The labeled fibers from the reuniens nucleus terminated in layers I, III and IV of the frontal cortex including the medial and ventrolateral orbital cortices, the cingulate cortex, and the infralimbic cortex. A few fibers from the nucleus reuniens also terminated in layer I of the agranular insular cortex, the temporal cortex and the parietal cortex. The labeled terminals were also present in the retrosplenial granular and agranular cortical regions of the layer I. The heavy PHA-L labeled fibers terminated in the stratum lacunosum and molecular of field CA1 of Ammon's horn of the hippocampus, and moderately in the subiculum, the presubiculum and the parasubiculum, mainly in the molecular layer. There were also may labeled fibers and terminals in the perirhinal cortex of layer I, the entorhinal cortex of layers I, III-IV and V, and the occipital cortex of layer I. These results indicate that the reuniens nucleus projects to much more widespread regions than previously known.