The sacroiliac joint (SIJ) is an accepted source of pain in patients with ankylosing spondylitis and other spondyloarthropathies, osteoarthritis, infections, and tumors, but the occurrence of isolated SIJ pain in the absence of such diseases is controversial. The term, sacroiliac joint dysfunction, which is used widely, describes pain from an SIJ that has no identifiable lesion but is presumed to have some mechanical etiology. Practitioners currently have no universally accepted gold standard for identifying a disc, facet joint, of SIJ as the pain generator. Treatment options for SIJ pain include medications, physical therapy, bracing, manual therapy, injections, radiofrequency neurotomy, and arthrodesis. Optimal management of patients with SIJ pain remains controversial. In the AMA Guides, Sixth Edition, a clinically established and causally related diagnosis of SIJ dysfunction is rated using the first row in Table 17-4. Surgery does not change the diagnosis or rating: The SIJ is not a motion segment of the lumbar spine, and SIJ fusion is not an alteration of motion segment integrity. Clinically, pain presumed to be from SIJ dysfunction is low back pain, so if this is the clinical diagnosis, the spine chapter in the AMA Guides, Fifth Edition, should be used. In such cases, the first step is to determine whether to use the diagnosis-related estimate or the range-of-motion method, and the article provides guidance about situations in which the use of each is appropriate.