A 19-year-old white woman with severe systemic lupus erythematosus developed symptomatic sacroiliitis early in her disease. Over the next 14 years she showed radiological progression of sacroiliitis. She had neither HLA-DR3 nor B27 antigens. The rare coexistence of SLE and ankylosing spondylitis may not be determined solely by genetic factors; sacroiliitis may be just an infrequent manifestation of SLE.