There are two common causes of left buttock pain and left leg pain: the first is pyriformis syndrome. The pyriformis muscle is located in the buttocks, and below it is the sciatic nerve. If the pyriformis muscle is cooled or inflamed, or if the pyriformis muscle is injured when doing strenuous exercise, congestion, edema, and inflammation will occur, and compress the sciatic nerve that is located below it, and then there will be left buttock pain and left leg pain, which radiates along the back of the thigh to the calf. The second type is lumbar disc herniation, which also presents with left hip and leg pain, but, at the same time, there is also lumbar pain, which radiates from the left side of the waist to the back of the thigh and the outside of the calf. However, there are also a few patients who do not have pain in the lower back, but only have pain in the left hip and left leg, and can go to the hospital for CT or MRI to make a clear diagnosis.