To investigate the mechanisms of dengue (DEN) virus transmission within the spinal cord, severe combined immunodeficient mice were intracerebrally inoculated with DEN virus type 2. After inoculation, a high virus titer and antigens were detected in the brain and spinal cord. At early stages of the infection, ultrastructural examinations showed that a few virions were present in the cytoplasm of ependymal cells lining the central canal. As the infection progressed, virions were observed in the lumen of the rough endoplasmic reticulum (RER), RER-derived vesicles and the Golgi region of infected neurons. These data suggest that the inoculated DEN virus might spread to the neurons of the spinal cord via the cerebral spinal fluid and cause several neuronal pathological responses. Moreover, DEN virus was also observed in myelinated and unmyelinated nerve fibers and typical neuronal synapses. Some virion-containing vesicles appeared to be fused with the membrane of presynapses, indicating that neuron-to-neuron transport of DEN virus might occur in the spinal cord. Additionally, anterior, lateral and posterior horns of the spinal cord exhibited different numbers of the positive neurons and different staining intensities of the DEN antigen during the infection. This difference likely represents variation of susceptibility to the DEN virus among the neurons of the spinal cord.