Acute peripheral nervous system diseases leading to paralysis in children are rare in Europe and the USA, whereas epidemics of a Guillain-Barré-like syndrome occur annually among children in rural parts of northern China. To clarify the features of this disorder 36 patients, aged 15 months to 37 years (median 7) with this syndrome were investigated; 91% were from rural areas. In 47%, a prodromal illness was reported in the preceding 4 weeks. Leg weakness and resistance to neck flexion were the earliest symptoms. The weakness ascended rapidly and symmetrically to affect the arms and respiratory muscles, with maximum weakness occurring a mean of 6 days after onset of weakness. Bulbar weakness occurred in 61% of patients, but only 1 had extraocular paresis. Respiratory assistance was needed by 31% of patients. Tendon reflexes were lost as weakness developed. 42% of patients had raised concentrations of protein in the cerebrospinal fluid, and the mean cell count was 3 cells/microliters (range 0-12/microliters). Electrodiagnostic studies in 22 patients showed severe reductions in motor evoked amplitudes from distal stimulation. Sensory action potentials were normal. Electromyography revealed denervation potentials in limb muscles. The distinctive epidemiological, clinical, and neurophysiological characteristics of this illness suggest that the disorder is different from both Guillain-Barré syndrome and poliomyelitis. The neurophysiological findings support the hypothesis that the disorder is a reversible distal motor nerve terminal or anterior horn cell lesion.