Background Polyneuropathies are infrequently described in cats. There is a genetic predisposition in several breeds. Objective To clinically characterize a novel motor polyneuropathy in a family of Siberian cats. Animals Thirteen closely related Siberian cats, 4 clinically affected and 9 clinically unaffected individuals. Methods Retrospective study. Clinical data and pedigree information were obtained from the medical records and breeder. Electrodiagnostic testing and muscle and peripheral nerve biopsy samples were obtained from 1 affected cat. Follow‐up information was obtained for all affected cats. Results Onset of signs was 4 to 10 months in affected cats. Clinical signs were progressive or waxing/waning neuromuscular weakness (4/4), normal sensory function (4/4), and variably decreased withdrawal reflexes (3/4). All cats returned to normal neurologic function within 1 to 4 weeks. All cats had a recurrence of weakness (3/4 had 1 recurrent episode, 1/4 had 3 relapses) from which they recovered fully. In 1 cat, electromyography and motor nerve conduction studies showed multicentric spontaneous activity, normal motor nerve conduction velocity, reduced compound muscle action potential amplitude, and polyphasia. Histologic evaluation of muscle and nerve in that cat showed mild muscle atrophy consistent with recent denervation, endoneurial and perineurial edema, and mild mononuclear cell infiltration within intramuscular nerve branches and a peripheral nerve. Pedigree analysis suggests an autosomal recessive mode of inheritance, although neither a genetically complex/polygenic condition nor an acquired inflammatory polyneuropathy can be ruled‐out. Conclusions and Clinical Importance We describe a motor polyneuropathy in juvenile Siberian cats characterized by self‐limiting weakness with potential relapse.