Case reports are presented on 2 patients whose illnesses started abruptly with severe subarachnoid hemorrhage associated with plexus meningioma of the lateral ventricle. The acute onset of headache, vomiting, stupor, and neck rigidity in these young patients, who had no previous symptoms, seemed to indicate aneurysmal origin of the hemorrhagic cerebrospinal fluid obtained on lumbar puncture. Carotid angiograms were made in both patients. Although hemorrhage with meningioma of the lateral ventricle seems not to have been reported in the literature, the authors believe that its occasional occurrence is probably responsible for clinical aggravation in some cases. In addition to acutely manifesting massive bleeding into the subarachnoid space, a second form is reported in which recurrent exacerbations thought to result from intermittent obstructive hydrocephalus were in fact due to repeated self-limiting bleeding from pathologic vessels within the ventricular cavity. This was confirmed in one of the authors" cases by the finding of xanthochromic cerebrospinal fluid on lumbar puncture and of organized blood clots adjacent to the tumor at operation. It is possible, at least in some of the cases of meningioma of the lateral ventricle with recurrently aggravating manifestations reported in the literature, that such a less acute form of bleeding occurred and that its rarity is more apparent than real. The mechanism of hemorrhage is briefly discussed.