Despite the fact that the craniospinal cerebrospinal fluid system forms a unique functional entity, most research studies are limited to analyzing only the cranial cerebrospinal fluid space and in a horizontal position, even though we spend most of our lives in an upright position (standing or sitting). We have showed in our previous studies that a transition from a horizontal to a vertical position lowers the intracranial pressure of the cerebrospinal fluid (CSF) to a subatmospheric value in accordance with the law of fluid mechanics and that changes in the intracranial pressure are not necessarily associated with a change of the intracranial volume as it is assumed by the classical hypothesis of CSF physiology. In our research, we studied how the change in body position affects the volume of the cerebrospinal fluid in the cranial and spinal parts of the cerebrospinal fluid system. Healthy volunteers of both sexes with an average age of 25 years were scanned in MRI in three different positions - in a horizontal position, a position with the head and upper body raised, and a position with the lower body raised; subsequently the cranial and spinal cerebrospinal fluid volumes were calculated using automatic segmentation methods for the cranial part and semi-automatic segmentation for the spinal part of the cerebrospinal fluid system. By comparing the volume of the cerebrospinal fluid between different positions, the results of our study show that the values of the total volume of the cerebrospinal fluid are significantly higher than reported in the literature and textbooks, and that changes in body position do not lead to a significant shift of the cerebrospinal fluid between the cranial and spinal spaces, as previously thought, but they primarily cause the redistribution of the cerebrospinal fluid within the spinal cerebrospinal fluid space, and primarily in the lumbosacral segment. Our research contributes to a better understanding of the physiology of the cerebrospinal fluid, which is of crucial importance for the treatment of numerous clinical conditions in which changes in volume and/or pressure occur within the cranial and spinal cerebrospinal fluid systems.