[1] This is different from organs that are not retroperitoneal, which have peritoneum on their posterior side and are suspended by mesentery in the abdominal cavity.

The retroperitoneum can be further subdivided into the following:[2] Structures that lie behind the peritoneum are termed "retroperitoneal".

It contains the following structures: Bounded by the posterior layer of peritoneum and the anterior leaf of the renal fascia.

Pararenal fat is a fatty layer situated posterior to the renal compartment, and extending inferiorly into the iliac fossa.

The most common type is a sarcoma followed by lymphoma, extragonadal germ cell tumor, and gastrointestinal stromal tumor/GIST.