This study will assess the efficacy of etanercept for the treatment of Ankylosing Spondylitis (AS).

Inclusion Criteria:

• Diagnosis of AS, as defined by Modified New York Criteria for Ankylosing Spondylitis, aged between 18 and 70 years of age.
• BASDAI greater than or equal to 40 (all scores on a scale of 0 to 100).
• Negative result of serum human chorionic gonadotropin (HCG) pregnancy test taken at screening in all women except those surgically sterile or at least 1 year postmenopausal.

Exclusion Criteria:

• Complete ankylosis (fusion) of spine.
• Previous receipt of etanercept, antibody to TNFα, or other TNFα inhibitors.
• Use of disease modifying antirheumatic drugs (DMARDs) other than hydroxychloroquine, sulphasalazine, and methotrexate within 4 weeks of baseline. Patients treated with hydroxychloroquine, sulphasalazine, and methotrexate may continue these drugs during this study but doses must be held stable for 4 weeks before baseline examination and for the duration of the study.