AbstractBackgroundSuspected immune‐mediated polyneuropathy has been increasingly reported in cats, especially in the last decade, but the condition remains poorly understood.ObjectivesRefine the clinical description and review the classification of this condition based on electrodiagnostic investigation and evaluate the benefit of corticosteroid treatment and L‐carnitine supplementation.AnimalsFifty‐five cats presented with signs of muscular weakness and electrodiagnostic findings consistent with polyneuropathy of unknown origin.MethodsRetrospective, multicenter study. Data from the medical records were reviewed. The owners were contacted by phone for follow‐up at the time of the study.ResultsThe male‐to‐female ratio was 2.2. The median age of onset was 10 months, with 91% of affected cats being <3 years of age. Fourteen breeds were represented in the study. The electrodiagnostic findings supported purely motor axonal polyneuropathy. Histological findings from nerve biopsies were consistent with immune‐mediated neuropathy in 87% of the tested cats. The overall prognosis for recovery was good to excellent, as all but 1 cat achieved clinical recovery, with 12% having mild sequelae and 28% having multiple episodes during their lifetime. The outcome was similar in cats with no treatment when compared with cats receiving corticosteroids or L‐carnitine supplementation.Conclusions and Clinical ImportanceImmune‐mediated motor axonal polyneuropathy should be considered in young cats with muscle weakness. This condition may be similar to acute motor axonal neuropathy in Guillain‐Barré syndrome patients. Based on our results, diagnostic criteria have been proposed.