To define the electrodiagnostic (EDX) features of Kennedy's disease, their distribution, their clinical correlation, and to determine whether they are unique to this disorder, we retrospectively evaluated the EDX and clinical features of 19 patients with Kennedy's disease and found that: (1) the percentage with sensory nerve action potential abnormalities is high (95%); (2) compound muscle action potential abnormalities are less frequent (37%) and less pronounced; (3) the needle electrode examination is always abnormal (100%), revealing acute and chronic motor axon loss, with the latter predominating; (4) the clinical onset is heterogeneous for both the site of onset (bulbar, upper extremity, lower extremity, combination) and the symptomatology (sensory, motor, sensorimotor); (5) focal onsets were reported in the majority (79%); and (6) there is a strong correlation between the clinical onset (both site and symptomatology) and the maximal EDX abnormalities. Thus, the EDX features of Kennedy's disease are consistent with a slowly progressive and very chronic degeneration of the anterior horn cells and dorsal root ganglia. Although the clinical onsets are heterogenous, the EDX features are homogenous and unique, consisting of a diffuse, very slowly progressive anterior horn cell disorder coupled with a sensory neuropathy/neuronopathy that mimics an acquired process.