In this study, we aimed to identify lung parenchymal changes in ankylosing spondylitis (AS) with high resolution computed tomography (HRCT). We prospectively studied 23 patients with documented AS. In ali patients, detailed clinical history including respiratory complaints are obtained. Follovving physical examination and pulmonary function tests (FEV1, FVC), HRCT imagining is performed in ali cases. The images are then analyzed for mediastinal, parenchymal and costovertebral changes. HRCT demonstrated pathology in 22 of the patients (95%). There were 8 patients with apical fibrosis and 1 patient with interstitiai lung disease. Thirteen patients had costovertebral fusion. Pulmonary function tests were normal in 12 patients, restrictive in 8 patients and obstructive in 3 patients. In conclusion, lung parenchyma in AS demonstrate a wide spectrum of changes from discrete nodules to severe fibrosis. A possible association betvveen interstitiai lung disease and AS exist; requiring vertical studies done with large patient groups.