Although memantine is widely used and generally considered safe, an abrupt cessation of memantine may result in discontinuation syndrome that can be distressing and result in decline of natural course. We report two patients who developed significant behavior disturbance after abrupt cessation of memantine. Although re-trial of memantine improves these symptoms, more additional drugs may be required to achieve previous status. Therefore, abrupt cessation of memantine should be prudent and require cautious follow up.