The spondyloarthropathies are a group of inflammatory arthritic conditions characterized by the absence of rheumatoid factor, and the presence of spondylitis, sacroiliitis, and an asymmetric peripheral arthritis. Familial aggregation and the presence of enthesitis, skin and mucous membrane lesions, bowel complaints, eye involvement, and aortic root dilatation are also features of these conditions. An association with HLA-B27 has been documented in the diseases constituting the spondyloarthropathies, including ankylosing spondylitis, Reiter's disease/reactive arthritis, psoriatic arthritis, and the arthritis of inflammatory bowel disease. Although there are similarities among the entities included in this group, each of these conditions have specific characteristics that help distinguish them. Differences in response to medications and in prognosis are such that it is important to make the correct diagnosis in the individual patient.