A case of neuro-cutaneous melanoma, in the course of which a bifocal melanoma of the cerebral hemisphere had developed, was used as a natural model for the study of the relation between tumorous and non-tumorous elements. The need is pointed out for the definition of such a cutaneous-meningeal syndrome before the development of a neoplasm. As tumours develop from the cells defining leptomeningeal melanosis, the possibility of a neuroradiological diagnosis of this process is accentuated, primarily by a minute examination of the sites characteristic of the disease. A premorbid detection of all such cases is imperative in order to introduce an early anti-tumour treatment.