The case of a 30 year old man who was believed to have a gastrointestinal motility disorder causing his chronic vomiting is reported. He had been well until 21 months previously when he had developed recurrent vomiting which would occur up to 10 times in a 24 hour period. Vomiting was not precipitated by eating and was not associated with any other symptoms. He had lost 25 kg in weight. A psychiatric assessment did not reveal a psychogenic cause for his vomiting. A brainstem magnetic resonance imaging scan revealed an area of low signal in the low midbrain just above the pons to the left of the midline. After gadolinium contrast injection the area enhanced. There was little or no mass effect, that is minimal displacement of normal structures, and minimal oedema. The appearance was that of a low grade or early brainstem tumour. There were no features of haemorrhage or infarct. The patient was managed with oral dexamethasone, resulting in prompt resolution of his symptoms. A search for a central neurological cause is recommended in a patient with unexplained persistent vomiting, even in the absence of other features to suggest a neurological problem. Autonomic function testing may provide additional information.