Study Comparing Etanercept 50 mg Once Weekly to 25 mg Twice Weekly in Patients With Ankylosing Spondylitis

Inclusion Criteria: * Diagnosis of AS, as defined by Modified New York Criteria for Ankylosing Spondylitis. * Active AS, defined by average of visual analog scale (VAS) of ≥ 30 for duration and intensity of morning stiffness and at least 2 of the following: VAS for patient global assessment ≥ 30; average of VAS for nocturnal and total pain ≥ 30; BASFI ≥ 30 (all scores on a scale of 0 to 100). Exclusion Criteria: * Complete ankylosis (fusion) of spine. * Previous treatment with etanercept, antibody to Tumor Necrosis Factor α (TNFα), or other TNFα inhibitors or other biologic agents. * Use of disease modifying antirheumatic drugs (DMARDs) other than hydroxychloroquine, sulphasalazine, and methotrexate within 4 weeks of baseline. Subjects 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. * Receipt of multiple nonsteroidal anti-inflammatory drugs (NSAIDs) at baseline. * Dose of NSAID changed within 2 weeks of baseline evaluation. * Dose of prednisone \>10 mg/day (or equivalent) or changed within 2 weeks of baseline evaluation.