Summary Objective: To evaluate the progression of ankylosing spondylitis (AS) as a function of disease duration and exercise frequency in a group of patients who were observed and followed up for six years. Methods: Detailed measurement of cervical, thoracic, and lumbar mobility together with measurements of posture and function were carried out in 28 patients (23 men, five women, mean age at final assessment 49.9 years) at two points separated by a period of six years. Anamnestic data on frequency of specific back and general exercises were also ascertained. Results: A significant deterioration was found in: Combined cervical rotation (initial mean 90°, final mean 36"). Cervical flexion/extension (66" to 42"). Combined cervical side flexion (41 O to 24"). Tragus-to-wall distance (1 70 mm to 224 mm). Chest expansion (60 mm to 20 mm). Combined lumbar side-flexion (49 mm to 18 mm). Modified Schober test (37 mm to 24 mm). Although functional deterioration occurred (disability score 1.33 to 1.59) this was not significant (p = 0.07). Anthropometric deterioration occurred independent of initial disease duration and reported frequency of exercise. Conclusion: These initial findings suggest that patients with AS experience progressive loss of movement independently of the duration of the disease and the reported frequency of unsupervised exercise. Further data are required using a wider spectrum of disease expression and more explicit information on spinal exercises, both supervised and unsupervised.