|Transverse section, showing the relations of the capsule of the kidney. (Peritoneum is labeled at center right.)|
|Human kidneys viewed from behind with spine removed|
The retroperitoneal space (retroperitoneum) is the anatomical space in the abdominal cavity behind (retro) the peritoneum. It has no specific delineating anatomical structures. Organs are retroperitoneal if they have peritoneum on their anterior side only. Structures that are not suspended by mesentery in the abdominal cavity and that lie between the parietal peritoneum and abdominal wall are classified as retroperitoneal.
The retroperitoneum can be further subdivided into the following:
- Perirenal space
- Anterior pararenal space
- Posterior pararenal space
Retroperitoneal structures 
Structures that lie behind the peritoneum are termed "retroperitoneal". Organs that were once suspended within the abdominal cavity by mesentery but migrated posterior to the peritoneum during the course of embryogenesis to become retroperitoneal are considered to be secondarily retroperitoneal organs.
- Primarily retroperitoneal:
- Secondarily retroperitoneal:
A useful mnemonic to aid recollection of the abdominal retroperitoneal viscera is SAD PUCKER, or DUKE CRAPS:
- S = Suprarenal glands (aka the adrenal glands)
- A = Aorta/IVC
- D = Duodenum (second and third segments [some also include the fourth segment] )
- P = Pancreas (tail is intraperitoneal)
- U = Ureters
- C = Colon (only the ascending and descending colons, as transverse and sigmoid retain mesocolon)
- K = Kidneys
- E = Esophagus
- R = Rectum
Another mnemonic going along with SAD PUCKER is 112 212111, this correlating to which ones are Primarily (1) or Secondarily (2) Retroperitoneal. Alternatively, PADD (Pancreas, Ascending colon, Descending colon, Duodenum) can be used to remember which structures are secondarily retroperitoneal.
Perirenal Space 
Bounded by the anterior and posterior leafs of the renal fascia. It contains the following structures:
Anterior pararenal space 
Posterior pararenal space 
Bounded by the posterior leaf of the renal fascia and the muscles of the posterior abdominal wall. It contains only fat.
Role in disease 
- Gray's Anatomy for Students, 2nd Ed. 2010. Pg. 251
- Ryan, Stephanie; McNicholas, Michelle; Eustace, Stephen (2004). Anatomy for Diagnostic Imaging. Sydney: Saunders. p. 191. ISBN 978-0-7020-2620-1.
- Kyung Won, PhD. Chung (2005). Gross Anatomy (Board Review). Hagerstown, MD: Lippincott Williams & Wilkins. p. 256. ISBN 0-7817-5309-0.
- K. L. Moore, A. F. Dalley, A. M. R. Agur (2005). Clinically Oriented Anatomy. Hagerstown, MD: Lippincott Williams & Wilkins. p. 1209. ISBN 0-7817-3639-0.