Left buttock and leg pain may be caused by physiological reasons such as overwork, or it may be caused by pathological factors such as trauma, lumbar spine degenerative disease, pyriformis syndrome and so on. 1. Overexertion: it is common that the symptoms of left buttock and leg pain may appear due to muscle exertion of buttocks and lower limbs caused by long time walking and stagnation of metabolic products such as lactic acid. 2. Trauma: left hip and lower limb fractures, blood vessel and nerve injuries due to trauma can cause left buttock and leg pain. 3. Degenerative diseases of lumbar spine: such as lumbar disc herniation, lumbar spinal stenosis and other diseases that cause pressure on the nerve roots innervating the lower limbs, the symptoms of left buttock and leg pain may appear. 4. Piriformis syndrome: Inflammation and edema of the piriformis muscle of the buttocks caused by cold and long-term strain injury, which squeezes the sciatic nerve and causes pain, numbness, and even impaired activity in the left buttocks and legs. Left buttock and leg pain may also have other causes, it is recommended to go to the hospital in time to clarify the cause of the disease, under the guidance of the doctor for treatment.