The SI joint pain has been noted to be present in up to 40 percent of patients with persistent pain after spinal fusion. The SI joint is the joint between the sacral spine and the ilium bones of the pelvis. There is one joint on each side. SI joint pain can be missed if there is not a high clinical index of suspicion to check for it. SI joint pain diagnosis involves use of confirmatory maneuvers that elicit SI joint pain and use of diagnostic injection of anesthetic into the joint. The diagnosis is confirmed if the anesthetic injection reduces pain by 75 percent or more. Treatment of SI joint pain includes specialized physical therapy and joint belts to improve joint alignment; adjunctive such as SI joint belts can be helpful. In severely refractory cases a new minimally invasive one hour SI joint fusion procedure was recently approved by the FDA and can be helpful in patients with intractable SI joint pain. Consultation with a surgeon trained in this new surgical approach is necessary for patients who have this type of problem.