Kidney pain facts. 1  The function and purpose of the kidneys are to remove excess fluid and waste products from the body. 2  The kidneys are located in the upper abdominal area against the back muscles on both the left and right side of the body. The function and purpose of the kidneys are to remove excess fluid and waste products from the body. 2  The kidneys are located in the upper abdominal area against the back muscles on both the left and right side of the body.