A 70-year-old man developed panhypopituitarism and was found to have hyperprolactinaemia and a locally invasive pituitary tumour. The visual fields were unaffected and therefore the patient was treated with hormone replacement only. After 3.5 years during which time the pituitary tumour had not enlarged further, the patient developed a mass in the left cerebello-pontine angle. This mass was subsequently shown to be entirely separate from, but histologically identical to, the pituitary tumour and the cells of both contained PRL. Evidence was obtained to show that the tumour had spread by a vascular route. This is the second reported case of a malignant prolactinoma.