This is a report of a glial brain tumor in a foetus at 7 to 8 months of intrauterine life, being the earliest reported case of a brain tumor. The tumor, growing in the medullary substance of the supramarginal gyrus and in the vicinity of the lateral ventricle, cannot be identified histologically with any known type of glioma, but appears to have originated from the matrix. As a special feature, this case is one of identical twins; the surviving twin has just reached the age of thirteen months and is healthy.