Worldwide, traumatic brain injury (TBI) is a major cause of death and disabilities. In United States, TBI is a serious public health problem since it contributes a third of all injury-related deaths. Despite a large number of clinical trials, no treatment exists for TBI so additional preclinical studies are needed to evaluate new therapies. In this study, an injury model developed by Marmarou and colleagues was used, that mimics a particular type of traumatic brain injury called diffuse axonal injury (Marmarou et al., 1994). The effectiveness of olfactory mucosal stem cells in the treatment of subacute traumatic brain injury was examined using a series of functional tests and analyses of brain sections. Inbred Lewis strains of rats were used so that cellular transplants are not rejected (Coyne et al., 2006). Behavioral results showed significant difference between the cell treated group and vehicle (saline) treated group in cognitive function and the qualitative histological analyses suggested lessened injury between the groups. Further investigation is required to understand the complete mechanisms behind the differences and the mode of action of stem cells.