The hydrodynamics of cerebrospinal fluid (CSF) is complex and is incompletely understood. We¹ and others² have documented enlargement of the fluid-filled cerebral ventricular system in astronauts following long-term missions (longer than 5 months) on the International Space Station compared with the normal appearance of the brain and ventricles prior to spaceflight. Astronauts who flew short-duration missions (1-2 weeks) on a space shuttle did not demonstrate a significant change in ventricular volume from preflight to postflight imaging.^1,2 Remodeling of cerebral structures in response to abolishment of the habitual gravitational stress of Earth implies a previously unrecognized gravitational dependency. Further investigation of the effect of gravity on CSF dynamics and the development of hydrocephalus may hold significance not only for astronauts but also for patients with CSF disorders on Earth.