A 43-year-old woman presented to our hospital with the complaint of a reddish-purple rash on the extensor sides of her forearms. She had been diagnosed with ankylosing spondylitis 7 years ago. On physical examination, reddish-purple nodules were detected on the pretibial areas of both legs and extensor sides of both hands and forearms. Neutrophil, eosinophil, lymphocyte, and mixed-type leukocyte infiltration and erythrocyte extravasation were observed in skin biopsy. Erythema elevatum diutinum (EED) was diagnosed. For treatment, sulphasalazine, colchicine, and diclofenac were started. After 3 months of treatment, the lesions were healed. To the best of our knowledge, this is the first report of EED coexisting with ankylosing spondylitis.