A 7-year-old, intact male domestic shorthair cat was presented with a progressive, non-weight-bearing lameness of the right forelimb. A neurological examination of the patient at the Small Animal Clinic revealed a paralysis of the radial nerve with sustained cutaneous sensation and a hyperaesthetic response. Further clinical, radiological and pathological findings lead to a diagnosis of a primary, neurotropic B-cell lymphoma in the brachial plexus.