A rare case of ankylosing spondylitis with interstitial pulmonary disease of the upper lung field, at an early stage in the disease, is described. The patient, a 35-year-old asymptomatic woman, was admitted to the hospital due to an abnormal chest radiograph that was found during preoperative evaluation for a toxic adenoma of the thyroid gland. Her mother and sister were also found to suffer from ankylosing spondylitis but without lung involvement. History, physical and laboratory examination as well as open lung biopsy excluded other causes of an interstitial pulmonary disease. The diagnosis of ankylosing spondylitis was based on clinical, radiographic, positive human leukocyte antigen (HLA-B27) and histologic findings.