The clinical investigations especially on symptomatology of 30 cases of the tumors of the lateral ventricle are carried out. For the clinical analysis, in agreement with Koos and Laubichler, the tumors of the lateral ventricle are classified into 2 groups, as follows: 1. Intraventricular tumors group (11 cases). 2. Paraventricular tumors group (18 cases). The following points are emphasized in the clinical features excluding radiological findings. 1. Because of symptomatologically no difference between the intraventricular tumors group and paraventricular tumors group, paraventricular tumors are included into the tumors of the lateral ventricle. 2. On neurological signs and symptoms, we contrast "false" localising signs which are common in patients with objective evidence of raised intracranial pressure and intermittent symptoms which occur more frequently with tumors in the ventricular system. 3. The results of surgical removal of the tumors are not always good. The diversity of results probably reflects the grade of malignancy and growth of the tumors, and skillfulness of operative technique is required, not to do damage to essential neurological elements and vital structures neighbouring the lateral ventricle.