A 22-year-old female noted a low grade fever and swelling of the cervical lymph nodes in May 1997, and later developed a dry cough. She was diagnosed to have interstitial pneumonitis, and then administration of corticosteroids alleviated her symptoms. On February 6, 1998, however, a high fever recurred and her swollen cervical lymph node on the right side was biopsied on February 9, 1998. A histological examination revealed an increased number of histiocytes and karyorrhexis of the lymphocytes in the paracortical areas, and she was therefore diagnosed to have histiocytic necrotizing lymphadenitis. She could not fully elevate her arm on February 16, 1998. On admission, her cervical lymph node was swollen on the left side. A neurological examination revealed a marked weakness of the right deltoid muscle, moderate weakness of the right latissimus dorsi, triceps and brachioradialis muscles and also a mild weakness of the serratus anterior, supra- and infra-spinatus, and biceps brachii muscles. The muscle power of the other muscles were normal and no muscle atrophy was evident. Winging of the right scapula was observed. The deep tendon reflexes were normal in all four limbs, and her sensation was also normal. No cerebellar sign was found. The Jackson, Spurling, Allen, Morley and Adson tests were all negative. ESR was mildly elevated to 18 mm/hr, but CRP was negative. RF, ANA and anti-SS-A and SS-B antibodies were positive, whereas LE-test, direct and indirect Coombs tests and other autoantibodies were negative. Needle EMG disclosed fasciculation potentials in the right triceps muscle and polyphasic waves in the right deltoid muscle. MRI showed gadolinium-enhancement of the right brachial plexus. Although an abnormal accumulation of gallium was detected in the right parotid and bilateral submandibular glands, no sicca symptoms were found and the Schirmer test findings were normal. Oral prednisolone (50 mg/day with gradual tapering) alleviated both her symptoms and the gadolinium-enhancement of the right brachial plexus. As a result, her right upper limb paresis was thus considered to have been caused by right brachial plexus neuritis, which was probably associated with histocytic necrotizing lymphadentis. Although acute cerebellar ataxia and meningitis have previously been reported to be complicated with histiocytic necrotizing lymphadenitis, this is the first report to describe the complication of peripheral neuritis with this condition.