Left-sided back and buttock pain can be caused by several reasons: first, rheumatoid spondylitis, which can be accompanied by pain in the lower back and pain in the sacroiliac joint above the buttocks, often on one side of the pain, early blood tests and spinal x-rays are needed for early diagnosis. Second, ankylosing spondylitis, ankylosing spondylitis patients can also appear waist and pain above the buttocks, often pain at the sacroiliac joint, often with morning stiffness and pain worsens in the morning, then to take early lumbar spine X-rays and sacroiliac joint X-rays, as well as blood tests for early diagnosis. Third, lumbar disc herniation, lumbar disc herniation can compress nerves and cause back pain and pain in the buttocks, so it is necessary to take CT and MRI of the lumbar spine at an early stage for early diagnosis and treatment. Fourth, lumbar spinal stenosis, lumbar spinal stenosis can also appear waist and buttock pain, then early spinal x-ray, CT, MRI to diagnose. Fifth, lumbar dorsal myofasciitis, lumbar dorsal myofasciitis patients can also appear lumbar pain, can be radiated to the hip, then early physical examination to early diagnosis.