Oculo-bulbar myasthenic symptoms as the sole sign of tumour involving or compressing the brain stem. Four patients with tumours involving or compressing the brain stem are described whose initial clinical symptoms of fluctuating paresis of the external ocular muscles and/or the pharyngeal muscles without other neurological deficits led to the primary diagnosis of focal myasthenia. The combination of an unusual clinical pattern, involvement of muscles of only one ocular nerve or severe dysphagia/dysarthria without extension of the myasthenic symptoms, should lead to further investigation to exclude other reasons of a focal myasthenic syndrome such as a brain-stem tumour. 