OBJECTIVE To evaluate flow patterns and anatomic appearances in the pelvic extraperitoneal spaces and to determine their relation to the abdominal extraperitoneal spaces. METHODS Helical computed tomographic (CT) guidance was used for injection of up to 1,000 mL of iodinated contrast material into one pelvic extraperitoneal space in each of five cadavers. Staged-volume injections into two prevesical spaces, one paravesical space, and one perivesical space were followed by helical CT. RESULTS The injected pelvic extraperitoneal spaces freely communicated with each other and with the perirenal and anterior and posterior pararenal spaces of the abdomen. This abdominal communication was via the large infrarenal space posteriorly and the circumferential extraperitoneal spaces about the peritoneal cavity bounded deeply and superficially by the parietal peritoneum and transversalis fascia, respectively. The contrast material reached the diaphragm superiorly and the femoral vascular sheath space and inguinal canals inferiorly. After crossing the midline both anterior and posterior to the peritoneal cavity, the contrast material reached the mesenteric root in four cadavers and the propericardial space of the thorax in two cadavers. CONCLUSIONS Intercommunication of the various extraperitoneal compartments occurs predominantly via the fascial-defined spaces, which contain mainly adipose tissue, but potential conduits exist through the communicating neurovascular structures where the fascia is anatomically perforated.