The most common causes of left leg and hip pain are over-exercise, sciatica, lumbar disc herniation, pyriformis syndrome, etc. If the symptoms persist, it is recommended to seek medical treatment in time. 1. Excessive exercise: If you have performed strenuous physical activities, it is easy to cause lactic acid to accumulate in the left leg as well as the buttocks, and the metabolic process of lactic acid may cause pain in the left leg and buttocks. 2. Sciatica: when the sciatic nerve is compressed for various reasons, pain in the buttocks and the back of the thighs will occur. Compression of the sciatic nerve is usually associated with lumbar disc herniation and bone spurs. 3. Herniated lumbar discs: Lumbar discs undergo degenerative changes with age, and the compression of the nerves can cause pain and numbness in the buttocks and lower limbs, as well as pain in the left leg and buttocks. 4. Piriformis syndrome: If the piriformis muscle is damaged or fatigued, it is easy to compress the sciatic nerve that runs underneath it, thus causing left leg and hip pain. Causes of left leg and hip pain are more reasons, may also be related to fasciitis, osteoarthritis, muscle strain and other diseases, if the symptoms continue to be unrelieved, it is recommended to go to the hospital in a timely manner by the doctor to find out the cause of the disease, for targeted treatment.