A patient with ankylosing spondylitis (AS) for 10 years suddenly developed localized midback pain after minimal activity. Although he sought immediate medical assistance, recognition of a septic spondylodiscitis was delayed 3 weeks. One day after admission, he developed fever and admitted to intravenous drug use. Staphylococcus aureus empyema and spondylodiscitis were subsequently diagnosed. Clinical differentiation of aseptic from septic spondylodiscitis cannot be ignored in patients with AS.