Objective. To obtain new evidence on the functional anatomy and anatomometry of the bladder. Subjects and methods. Magnetic resonance imaging (MRI) scans were analyzed in 100 patients; of whom 15 were adolescents (18—21 years) and 85 were adults (21—59 years). MRI scans were obtained on a Magnetom Symphony 1.5 T scanner (Siemens, Germany). The sampling criteria were the absence of space-occupying lesions (cysts, cancers, benign prostatic hyperplastic nodules, etc.) in the pelvic cavity and adjacent organs, as evidenced by MRI. The shape and size of the bladder, its filling degree and wall thickness were estimated. Results. The bladder is variable in size and shape; its linear dimensions can differ by more than twice in weak and significant filling states. The vertical size is most variable (from 4.1 to 8.7 cm in adolescence and from 3.7 to 6.9 cm in adulthood, as shown by the mean values); a less variability is shown by the sagittal size (from 6 to 9.1 cm in adolescence and from 6.9 to 9 cm in adulthood) and the frontal one (from an average of 7.4 to 9.2 cm in adolescence and from 7.3 to 8.6 cm in adulthood). The bladder can be polygonal, crescent, pyramidal, spherical, and ovoid in shape. Conclusion. During the increased filling of the bladder, there is substantial thinning of its walls, mainly the lateral walls, by 1—3 mm, with the lowest values at maximum filling. Bladders that are rounded in outline and those that are ovoid and spherical in shape are most frequently commonly encountered during significant filling; polygonal and crescent-shaped bladders prevail during weak filling. With a similar degree of filling of the bladder, no statistically significant differences were found in its sizes and wall thickness in adolescence and adulthood.