Three cases of brain stem astrocytoma and one of a para-stem vascular tumour are described, each showing a history of relapses and remissions. The diagnoses were confirmed by necropsy, and it is suggested that the relapsing course may have been due to oedema and necrosis in both the tumour and the surrounding brain tissue. Features indicating repeated recurrence of a lesion at the same site in the brain stem justify full neuroradiological investigation before a diagnosis such as multiple sclerosis can be accepted.