Acute brachial neuropathy (ABN) is a rare disease, characterized by an acute or subacute onset of pain followed by weakness of shoulder or arm muscles without trauma or traction injury. So the diagnosis of this clinical entity is not easy. The purpose of this study was to analyze retrospectively the ABN in 14 cases focusing on the clinical profile and to evaluate the effectiveness of electrophysiologic study in diagnosis of ABN with a new result helpful in localizing a brachial plexus disorder. The most helpful electrophysiologic data of ABN in my patients seemed to be abnormalities of low amplitude, abnormal right to left difference of compound motor action potentials (CMAPs) and sensory nerve action potentials (SNAPs) in axillary nerve, ulnar or median nerves. Results of nerve conduction velocity, terminal and F-wave latency were not as useful. But the electromyogram was most helpful in localization of upper or lower plexus lesions and cervical radiculopathy. The most striking clinical feature of ABN was the rapid onset of pain followed by the development of muscle weakness of shoulder girdle after a variable period or within four days. In contrast to other reports, intrinsic hand muscle weakness was observed in 3 cases with sensory changes in ulnar nerve distribution. The cervical radiculopathies (C5-C7 roots) were simultaneously combined with ipsilateral axillary neuropathy in 3 cases. In this study, decreased amplitude, abnormal right to left difference of SNAPs and CMAPs, and neurogenic EMG findings with normal data of NCV, terminal and F-wave latencies suggest that the pathology of ABN might not be a demyelinating process, but axonopathy.