The authors report an unusual case of myelodysplastic syndrome (MDS) associated with ankylosing spondylitis (AS). A 40-year-old-man with MDS presented with chronic low back pain for 6 years. Four years ago, MDS was diagnosed during routine blood analysis for the work-up of his articular complaints. His initial articular complaints were attributed to extramedullary manifestations of MDS. Persistent low back pain with increasing intensity finally led the patient to seek medical attention. Radiograph of the pelvis showed bilateral asymmetric sacroiliitis. A diagnosis of AS was established on the basis of modified New York criteria. Although various autoimmune phenomena associated with MDS have been described, this is the first report of AS in the setting of MDS. Causal relationship between these two disorders is currently unknown. Increased risk of hematological diseases as well as AS in individuals with a positive HLA-B27 provides a feasible explanation for this rare observation.