The case of a 14-year-old girl who had severe subarachnoid bleeding as the first manifestation of a benign astrocytic tumor of the lateral aspect of the third ventricle is reported. Tumors that cause bleeding are usually neuroectodermal tumors in children and malignant tumors in adults. A review of the literature serves as the basis for a discussion of the frequency of bleeding as the first manifestation of brain tumors (1 to 10%) and of the pathogenesis of these hemorragies for which three theories (vascular, mechanical, and metabolic) have been put forward.