External lumbar drainage (ELD) is recognized as a screening method for ventriculo-peritoneal shunting (VPS) candidacy for possible normal pressure hydrocephalus (NPH). This study focused on the ELD predictability of the cognitive outcome after VPS for NPH. In addition, Repeatable Battery for the Assessment of Neuropsychological Status (RBANS) was examined in ELD cognition screening. ELD results were considered positive with any improvement in gait and/or cognition. Among 36 patients examined for possible NPH, 26 underwent VPS because of positive ELD. Cognitive outcome after VPS was assessed at 6-month follow-up. The RBANS scores, examined pre- and post-ELD, were evaluated statistically to identify consistency with the neuropsychologist judgment and the predictability of cognitive outcome after VPS. Among 26 shunted patients, gait was improved in 24. Cognitive improvement was rated in 19, and there were 9 false negative and 5 false positive in ELD cognition screening. The neuropsychologist judgment in ELD cognition screening is most consistent with the RBANS score in delayed memory. The patients rated as improved in cognition after VPS had significantly lower RBANS scores pre-ELD in immediate memory and delayed memory. If both scores at pre-ELD were ≤ 80 (13 patients), all were rated as improved in cognition after VPS. ELD screening was highly predictive of clinical gait improvement but not of cognitive improvement after VPS for possible NPH. Particularly among patients with a positive ELD gait response, pre-ELD low RBANS scores in memory predicted cognitive improvement after VPS. RBANS seems effective in evaluating cognition for NPH.