We reviewed 36 traumatic brachial plexus injury patients with C5 nerve root injury. We used the choline acetyltransferase (CAT) activity measurement as a gold standard indicator of repairability to assess the reliability of the conventional techniques (preoperative clinical, electrophysiologic, and radiologic examination and intraoperative clinical and electrophysiologic examinations). We proposed a repairability scoring system composed of the correlated conventional techniques and tested the validity of this scoring system using the same reference technique (CAT activity measurement). We found no significant correlation between sensation at C5 dermatome and electromyography study with C5 repairability. On the other hand, we found a significant correlation of Tinel sign, myelography, macroscopic and microscopic examination, and electrical stimulation with C5 repairability. Based on these results, we propose a simple 21-point scoring system to evaluate the repairability of C5 nerve root that is composed of Tinel sign, myelography, macroscopic and microscopic appearance, and electrical stimulation. The scoring system was found to be highly significantly correlated with C5 repairability. We concluded that our proposed evaluation scoring system is a reliable method for C5 repairability evaluation, and it can replace sophisticated techniques.