Objective To retrospectively investigate the various etiologies of foot drop and the value of differential diagnosis by electromyography in patients with foot drop.Methods A total of 155 patients who visited our department due to foot drop from September 2011 to June 2015 were enrolled and met the criteria for muscle strength of foot drop. The findings of conventional nerve conduction examination and needle electromyography were analyzed.Results Electrophysiological results showed 70 cases of peroneal mononeuropathy, 9 cases of sciatic neuropathy, 19 cases of polyneuopathies, 9 cases of lumbosacral plexopathy, 42 cases of L₅/S₁ radiculopathy, and 6 cases of motor neuron disease. Among the cases of peroneal mononeuropathy, 72.8% (51/70) were entrapment lesions at the fibular head, and the other cases (27.2%) were caused by other reasons; electrophysiological results also showed that conduction block across the fibular head, reduced velocity, and axonal damage accounted for 71.4%, 2.9%, and 25.7%, respectively (P<0.05). In the patients with polyneuropathies and lumbosacral plexus radiculopathy, foot drop was the concomitant symptom, and in one patient with motor neuron disease, foot drop was the initial symptom.Objective Although nearly half of the cases of foot drop diagnosed in the department of neurology are caused by peroneal mononeuropathy, it is necessary to pay attention to the lesions at other levels of motor neurons in differential diagnosis, especially the possibility of systemic diseases, which is essential for treatment and prognostic evaluation. Nerve electrophysiology can be used to determine the level and distribution of nerve lesions and thus to provide some clues for etiological analysis.