Spontaneous motor and sensory recovery was followed up for more than five years after the injury in 90 cases of brachial plexus injury, which were seen in the Orthopaedic Department of Niigata University and its affiliated hospitals but in which no positive treatment had been given because of various situations. 87 adults and three children composed of those cases. The formers consisted of nine cases of upper postganglionic type, one of lower postganglionic, 50 of whole postganglionic and 27 of whole preganglionic, and the latters did of two of whole postganglionic and one of whole preganglionic. Muscles innervated through brachial plexus were grouped into 15 by particular specific function and a muscle group having the power of MMT-3 or more was assessed as recovered or preserved function. In whole postganglionic type, longer the time elapsed after the injury more muscle groups recovered and 90% of muscle groups had recovered to MMT-3 and more by one and half year after the injury, revealing overall prognosis of motor recovery being good. In whole preganglionic type, only very small number of muscle groups recoverd, mostly within 4 months after the injury. In upper postganglionic type, overall recovery was good. Based on the follow-up results described above, the indication of operative reconstruction was considered as follows. In whole postganglionic type, non-recovering muscle group at 4 months can still spontaneously recover but the non-recovering muscle group with MMT-0 at 10 months should be surgically reconstructed except the muscle groups innervated through upper roots. Surgical reconstruction is indicated for infraspinatus, thumb-opponens and adductor among muscle, groups with MMT-2 at 10 months. Surgical reconstruction is indicated for all muscle groups with MMT-0 to 2 at one and a half year. In whole preganglionic type, surgery is indicated for muscle group with MMT-0 to 2 at four months especially for thumb-opponens and adductor. Children showed good recovery in the long run, therefore too early surgery should be warned.