With regard to the lower two thirds of both kidneys, the lateral aspects rest on the aponeuroses of the transversus abdominis muscles; the central aspects rest on the quadratus lumborum muscles; and the medial aspects rest on the psoas muscles.

The psoas muscles take an oblique course from the lumbar vertebrae to the femurs, displacing the kidneys laterally. Because the right kidney lies inferior to the left kidney, it is generally displaced farther from the midline.

On each side, two or three nerves pass posterior to the psoas muscle, emerge from its lateral border, then travel between the kidneys and the aponeurosis of the transverse abdominis as they descend obliquely to the inguinal region. In craniocaudal order, these are the subcostal (T12 spinal) nerve and the L1 spinal nerve or its terminal branches—the iliohypogastric and the ilioinguinal nerves.