The kidneys are located on the back side of the body, just below the rib cage on either side of the spine. They are positioned in the retroperitoneal space, which means they lie behind the peritoneum (the lining of the abdominal cavity) and against the posterior abdominal wall. Specifically, the kidneys are situated between the levels of the T12 and L3 vertebrae, with the right kidney generally positioned slightly lower than the left due to the liver's presence. The upper portions of the kidneys are somewhat protected by the 11th and 12th ribs. Because the kidneys rest against the muscles of the lower back, distinguishing kidney pain from general back pain can sometimes be difficult.
In summary, the kidneys are located on the back, beneath the lower ribs, lateral to the spine, and somewhat protected by the lower ribs and back muscles.