Neurologic complications after surgical treatment of clavicular nonunion were rare, and they were usually types of incomplete paralysis of one or more branches of brachial plexus. We experienced a complete brachial plexus paralysis of whole arm type developed after compression plating and bone grafting for infectious clavicular nonunion. This 44 years old male patient, sustained infectious clavicular nonunion of mid-shaft, complains postoperatively complete paralysis of right upper extremity and severe burning pain around the clavlcle. We performed exploration after 1 day of operation. The operative findings are no gross damage of brachial plexus, direct compression with cancellous bone graft, narrowing of costoclavicular space and fibrotic adhesion with surrounding soft tissue. For decompression of brachial plexus, we perform adhesiolysis and neurolysis, and refixed the clavicle after plate bending along anterosuperior curvature and removal of inferiorly grafted bone to restore costoclavicular space. Eletrodiagnostic study in two weeks reveal severe brachial plexopathy of whole arm type. After three months of operation, he regain the nearly complete function of upper extremity and radiologic study show a evidence of bony union. The obtained results from the evaluation of this patient were as follows: 1. Direct compression by cancellous bone graft and a spike of bone is a major contributing factor. 2. Fibrous adhesion with surrounding soft tissue due to previous infection is another important factor of reducing the costoclavicular space. 3. Motor function is more profoundly affected than sensory function, and the order of motor return is radial, median, musculocutaneous, axillary and ulnar nerve. 4. When brachial plexopathy follow immediately operation of clavicle, early exploration is indicated for diagnostic and therapeutic purpose.