Osteoid osteoma is one of the infrequent causes of musculoskeletal pain. Rheumatic diseases such as ankylosing spondylitis are considered especially in cases of bilateral sacroiliitis. An association between these diseases is uncommon. Since both osteoid osteoma and sacroliitis response well to antiinflammatory therapy, radiological investigations, such as computed tomography (CT), have a significant role in diagnosis due to its superiority in visualizing the osseous tissue. Thus, this rare condition can not only be diagnosed, but also managed. This report presents a case of bilateral sacroiliitis in association with osteoid osteoma in a 23-year-old male patient, who was diagnosed and treated initially as bilateral sacroiliitis. CT was performed in order to evaluate the sacroiliac joint space and the accompanying osteoid osteoma was detected coincidentally. Turk J Phys Med Rehab 2010;56:152-4.