The authors discuss the criteria of differential diagnosis for a correct use of the term "multiple meningiomas". Reviewing a series of 934 meningiomas, of which 834 were intracranial and 100 were spinal, they found 14 cases of multiple meningiomas, i.e. an incidence of 1.5%. The study shows that multiple meningiomas are quite similar to solitary meningiomas in all their biological characteristics. Furthermore, the possible presence of more than one meningioma must always be kept in mind in the clinical and radiological evaluation of a patient. The aetiology of multiple separate meningiomas is discussed: the hypothesis which suggests their origin from multicentric neoplastic foci activated by a supposed "tumour-producing factor" appears to be the most reliable.