Background and Purpose. Few randomized controlled studies have examined the effects of exercise in patients with ankylosing spondylitis (AS). This study investigated the effects of a 12-week, multimodal exercise program in patients with AS, Subjects. A convenience sample of 30 patients with AS (18 male, 12 female), with a mean age of 34.9 years (SD=6.28), participated in the study. Twenty-six subjects were classified as having stage I AS and 4 subjects were classified as having stage II AS according to the modified New York Criteria. Methods. This study was a randomized controlled trial. Subjects were assigned to either a group that received an exercise program or to a control group. The exercise program consisted of 50 minutes of multimodal exercise, including aerobic, stretching, and pulmonary exercises, 3 times a week for 3 months. Subjects in both groups received medical treatment for AS, but the exercise group received the exercise program in addition to the medical treatment. All subjects received a physical examination at baseline and at 12 weeks. The examinations were conducted under the super-vision of a physician who specialized in physical medicine and rehabilitation and included the assessment of spinal mobility using 2 methods: clinical measurements (chin-to-chest distance, Modified Schober Flexion Test, occiput-to-wall distance, finger-to-floor distance, and chest expansion) and inclinometer measurements (gross hip flexion, gross lumbar flexion, and gross thoracic flexion). In addition, vital capacity was measured by a physiologist, and physical work capacity was evaluated by a doctorally prepared exercise instructor. Results. The measurements of the exercise group for chest expansion, chin-to-chest distance, Modified Schober Flexion Test, and occiput-to-wall distance were significantly better than those of the control group after the 3-month exercise period. The spinal movements of the exercise group improved significantly at the end of exercise program, but those of the control group showed no significant change. In addition, the results showed that the posttraining value of gross thoracic flexion of the exercise group was significantly higher than that of the control group. Physical work capacity and vital capacity values improved in the exercise group but decreased in the control group. Discussion and Conclusion. in this study, a multimodal exercise program including aerobic, stretching, and pulmonary exercises provided in conjunction with routine medical management yielded greater improvements in spinal mobility, work capacity, and chest expansion.