Degenerative disease of the sacroiliac joint is common in middle-aged and elderly patients. Its radiographic features simulate those of ankylosing spondylitis. Interosseous space narrowing, subchondral sclerosis, and osteophytosis are apparent. Although intraarticular bony ankylosis is generally absent, anterior paraarticular bridging osteophytes resemble true osseous fusion of the joint cavity on frontal radiographs. Focal sclerosis in degenerative disease is most common on the superior and inferior margins of the articular cavity and can usually be differentiated from that accompanying ankylosing spondylitis and osteitis condensans ilii.