The sciatic nerve is the largest nerve in the body. It is formed by nerve roots coming out of the spinal cord in the lower back. The nerve goes down through the buttock, and then its branches extend down the back of the leg to the ankle and foot.

A herniated disc may press on one or more of the nerve roots that form the sciatic nerve. Pressure on one of these nerve roots will often cause symptoms of sciatica, such as pain, numbness, weakness, and tingling in the affected leg.

A herniated disc is the most common cause of sciatica. But sciatica can also be a symptom of other problems. These include a narrowing of the spinal canal (spinal stenosis), pressure on a nerve root from an injury, and certain rare tumors.