Spinal cord injury (SCI) invariably results in the loss of neurons and axonal degeneration at the lesion site, leading to permanent paralysis and loss of sensation. There has been no successful treatment for severe spinal cord injuries to recover back to normal function yet. Studies have shown that the transplantation of stem cells may provide an effective treatment for SCI because of the self-renewing and multipotential nature of these cells. Stem cells have the capability to repair injured nervous tissue through replacement of damaged cells, neuroprotection, or the creation of an environment conducive to regeneration by endogenous cells. Up to today several types of stem cells have been transplanted into the injured spinal cord. However, the question of which cell type is most beneficial for SCI treatment is still unresolved. There are still several limitations to the current data sets which require further investigation. Anat Rec, 2010. © 2009 Wiley-Liss, Inc.