Traumatic Brain Injury (TBI) is defined as an injury to the brain parenchyma resulting in neurological deficit following a trauma. Cell transplantation has evolved as a novel treatment modality in the management of TBI. Autologous Bone Marrow Mononuclear Cells (BMMNCs) have shown beneficial effects in the functional recovery of neurological deficits. We present a case of a 15 year old female who suffered from a TBI due to a road traffic accident, 7 years ago. She underwent two doses of intrathecal transplantation of autologous BMMNCs for chronic TBI. No severe adverse events were noted. She showed improvements in her speech, cognitive abilities, memory, higher function and fine motor skills. PET CT scan was used as a monitoring tool to evaluate the effect of cellular transplantation at a cellular level. On comparing the PET CT scan brain performed 6 months after the intervention with the previous scan, increased metabolic activity in various areas of the brain was observed. These changes also correlated to the functional improvements observed in the patient. Hence, stem cell transplantation may have a promising future as a therapeutic intervention in chronic TBI.