A NUMBER of observers have reported untoward reactions following lumbar puncture in patients with tumors of the brain or with increased intracranial pressure due to other causes.* These untoward reactions have been attributed to temporal lobe herniation or herniation of the cerebellar tonsils. In some of the cases death is reported to have occurred immediately from presumed compression of vital centers, and in others a train of symptoms have developed which are presumed to indicate a more gradual compression. The statement is frequently seen that lumbar puncture is dangerous and is contraindicated whenever papilledema is present. This conclusion is reached on the basis of untoward reactions in individual cases, and to our knowledge there has not been an analysis of the results in a large series of cases. This study was undertaken in order to determine the frequency of untoward reactions in a large series of patients with tumors of