Twenty-one cases of neuralgic amyotrophy referred for diagnosis and for electromyography were studied. The criteria used for diagnosis included pain, wasting and paralysis of shoulder girdle muscles, the absence of a compressive or traumatic lesion, spontaneous full or partial recovery and electromyographic findings of denervation or reduced numbers of functioning motor units of the muscles involved. Pain was usually sudden in onset and preceded paralysis. The commonest muscles involved were the deltoid, supraspinatus, infraspinatus and biceps. Sensory changes were minimal. Recovery was the rule and repeat electromyogram after full clinical recovery was normal. The common diagnostic difficulties were excluding poliomyelitis in children, trauma in adults and cervical spondylosis in the elderly. The atypical manifestations need to be recognised in this condition, the aetiology of which is unknown in the majority of cases.