INTRODUCTION: Demonstration of the safety of human neural stem cells is critical for the overall development of intramedullary transplantation following spinal cord injury (SCI). We present interim results of an on-going Phase I/II trial 12 months after transplantation of human CNS stem cells (HuCNS-SC®, StemCells, Inc., Newark, California) in patients with chronic thoracic (T2-11) SCI. Special emphasis will be put on aspects of surgical administration and methods of thoracic segmental assessment. We will also address preliminary clinical neurophysiological and radiological outcomes following stem cell transplantation. METHODS: Three ASIA Impairment Scale (AIS) A paraplegic patients were transplanted with allogenic HuCNS-SC cells between 3-12 months post-injury. RESULTS: There were no surgical complications or adverse changes directly attributed to the cells at the 12 months follow-up. Signs of segmental improvement were observed in 2 out of 3 AIS A patients, and the third subject remained stable. Based on the safety results in the first AIS A patients, recruitment of patients with incomplete injury (AIS B and C patients) has now commenced. CONCLUSION: We present 12 months interim safety and preliminary efficacy data of the first 3 AIS A SCI patients who underwent thoracic intramedullary transplantation of HuCNS-SC as part of an on-going open-label Phase I/II trial.