The flank is the area on the sides and back of your abdomen, between your lower ribs and your hips. Pain in this area is called flank pain. Several injuries, diseases and infections can cause pain in the flanks. Flank pain can range from mild to severe. Flank pain affects the area on either side of the lower back, between the pelvis and the ribs. Pain in the flanks can result from several conditions, diseases and injuries. Kidney stones, infection and muscle strains are common causes of flank pain.