OBJECTIVE Increased intracranial pressure (ICP) that is refractory to medical measures and ventriculostomy placement after severe traumatic brain injury or aneurysmal rupture is associated with high mortality. In some recent reports, authors have described the use of lumbar cerebrospinal fluid drainage in these patients. We report the results of a prospective study involving the use of lumbar drainage in 15 patients with elevated ICP that was refractory to medical management and ventriculostomy placement. METHODS A prospective study was designed to enroll patients at Loma Linda University Medical Center. Ten patients with traumatic brain injury and five patients with ruptured aneurysms were enrolled. Medical management included maintaining serum Na >150 mEq/L, mild hyperventilation, deep sedation, and maintenance of normothermia. A lumbar drain was placed when ICP was >20 mm Hg for an average of 3 hours despite the optimization of the aforementioned parameters. RESULTS After lumbar drain placement, ICP was reduced from a mean of 28.2 ± 6.5 mm Hg to 10.1 ± 7.1 mm Hg (P <0.001). Requirements for hyperosmolar therapy, sedatives, and paralytics were also significantly decreased (P < 0.05) after lumbar drain placement. One patient had unilateral papillary changes four hours after lumbar drain placement. The pupil returned to its normal state after decompressive craniectomy. There was no incidence of CSF infection. Three of the 15 patients died during the study period. CONCLUSIONS This study shows the beneficial role of lumbar cerebrospinal fluid drainage as an effective and safe treatment modality for elevated ICP.